Panchanon Bhattacharya (1853–1919), a disciple of Lahiri Mahasaya (1828–95), was permitted by him to publish many of Lahiri's commentaries on significant texts in Hinduism, including the Yoga Sutras. The book is a terse sort of primer in a composite form of yoga. Bhattachariya states that the book's content is not understandable to other than yogis. He also writes that some of the statements of Lahiri Mahasaya were not intelligible even to his disciples. [cf. Iv 131] (3)
When a yogi says "This yoga is a science," first give a thought to "science matters". It matters to know the word 'science' has many meanings and many shades of meaning unless meanings are well specified. The yogi could mean, "This yoga stands out from ignorance (it is a body of knowledge, ways and doctrines - that sort of old 'science')" Or what he intends to say, could be "This yoga covers general truths that you can test thoroughly or systematically yourself by the methods devised."
Kriya practice is also a form of art: According to one good definition of art, it is something that is made and/or displayed with the intention of it being art. On a smaller scale, art is "the expression or application of human creative skill and imagination . . . producing works to be appreciated." Art is also skilled doings, typically through practice. Skill and adeptness may go into art. (Oxford Dictionaries). The art of living is wise to master as well.
The Yoga Sutras of Patanjani is divided into four chapters. The numbers in brackets below refer to verses (sutras) of Patanjali, not to pages.
You may notice that Lahiri tells about kriya yoga. Much of what we are dealing with is Lahiri teachings effected by Yoga Sutra passages.
Abandon expectations for results. [cf. 31]
Note. Buddha teaches that the good results from meditation - or fit meditation - derive from the fit practice and proper instructions given, and having thoughts or expectations in between meditations or even for some time during them may be of little consequence. [Bhumija Sutta]
There are sound expectations and other expectations: expectations outside the meditation sessions and expectations while meditating. If you can handle both sorts of expectations, good. Research on meditation helps the former, and good methods help with the latter: In the ancient Bhumija Sutta, Buddha teaches it is the fit method that matters, not expectations or no-expectations. Meditating all right is better than being distracted by expectations or other irrelevant thoughts during a session.
Be as "classy" as you can: Before choosing a meditation method or system of methods, find out which methods come out on top among the researched methods, and thereby may be the method to expect the most from, as judged from averages that research findings are typically based on.
During meditation sessions we could aim at just doing the methods all right. Maharishi Mahesh Yogi teaches sound ways to do it. [◦TM Site]
Objects look void in some states of yoga. [cf. 43]
Established in the Self, the heart becomes one with the Self. [cf. 41]
Beyond time is the inner Self that is greater than the Creator. [cf. 26]
The calm, great state is more easily gained through great disinterest. [cf. 37]
The contemplative is to hold onto the Self. [cf. 33]
The Self is above the results of bad actions. [cf. 24]
Train awareness of the heart inside the mind. [cf. 30]
The pure and those free of reasoning, win the grace of Self in their lives. [cf.
Yogic liberation is the ultimate Self. [cf. 51]
Inner wisdom is called illumination. [cf. 36]
Indifference is to be developed in very many cases. [cf. 33]
2. Practice to awaken in the
subtle Self, needs to end up subtle, at least
Being ineffective, in doubt, lethargic and unstable distract the yogi. [cf. 30]
The seeker is to develop disinterest. [cf. 16]
Unwillingness to do good yoga, and wrong notions, are hindrances of yoga. [cf. 30]
Great contentment is to be sought on top of righteousness. [cf. 33]
Practice to make the mind focused, i.e., one-pointed. [cf. 32]
Subtlety is the gist. [cf. 45]
The heart calms down through yogic pranayama. [cf. 34]
The seed of omniscience is holding stably onto the inner Self, cultivating it. [cf. 25]
The state of calm can be had by dreams and drowsy feelings. [cf. 38]
Wisdom may be blessed by the grace of the Self. [cf. 49]
3. The sound of OM (AUM) reaches into Selfhood
Looking steadfastly upwards like a fool can be a clear sign of yoga trance. [cf. 1]
Reverence is generated by doing kriya [cf. 20]
The sound of OM is also known as pranava (pranaba). One should listen in to it. [cf. 27]
Keys to sound progress in meditation is the fit method, being fairly instructed, and then comes skilful practice over and over. Selfhood can be developed. It takes time. There are plotters who teach differently.
The sound or vibe of OM (AUM) . . . there are methods for becoming aware of it. But mark the caveat: Guru Dev says that for those in the householder stage of life, meditation on OM "does not give good effects, it will be responsible for decline and misfortune." (in Mason 2009, 323-24)
Don't get harmed and freaked out: Keep your day-to-day practice within the "vital sustainability" in your case. That is, within what you can safely endure with much ease.
The Deep Seer needs to be strong to suffer troubles stemming from common
people who do not understand a word of what he says.
1. Far-out knowledge is somehow
attuned to the Hovering Self
From great purity Divinity can [at last] be generated, and the capacity for
realizing the Self. [cf. 41]
When truth is established, kriya becomes fruitful. [cf. 36]
Enlightenment starts, and much wisdom can be attained. [cf. 148]
Knowledge of far-away-places can be had from looking steadfastly into the third eye
in the forehead. [cf. 45]
By burning the seeds of suffering one goes to the ultimate Self. [cf. 10]
Ignorance . . . is a root of troubles in life. [cf. 5]
Righteous action can and should result in happiness. [cf. 14] [
To ordinary people mind tricks still exist. [[cf. 22]
Hatred is due to ignorance 
2. The Deep Seer is strong to
By [common] contentment much happiness can be had. [cf. 42]
But the man of Knowledge considers all states of manifestation to be sorrow. 
The Deep Seer is consciousness. [cf. 20]
Do kriya to attain samadhi. [cf. 2] [
The seer and seen are the unreasonable association [cf. 23]
By doing Patanjali yoga, impurities are purified to enrich righteousness. [cf.
3. Common people do not see too
Cultivating good sentiments is necessary for removing doubts about how to live and
regulate one's life (yama and niyama, do's and don'ts). [cf. 33]
Through purity one tends to dissociate from others. [cf. 40]
Ordinary people do not see the hollowness of the world's appearance. 
What is seen is meant for enjoyment of the seer. 
Anger stemming from sorrow is called hatred [cf. 8]
Deep knowledge may or may not harm the one that brings it out in the open. What
sorts of fruits deep realisations bring, depend on many influences including how
many there are around to share them.
Common people do not always understand there is a need to take serious and at least try to live up to what they understand might be wise, not to say necessary. Warnings of global warming is a good example of that sort of mass shirking.
1. By meditation, gain in Selfhood
Start practicing to make the mind one-pointed. [1:32]
By the practice of pranayama, gradually dharana (focus) is formed. [2:53]
NOTE. The reverse is also true: In deep meditation kriyas (pranayama) come spontaneously.
From purity [santosha] are generated divinity, tranquility, concentration. [2:41]
NOTE. Santosh(a) means contentment and satisfaction, and not purity.]
By concentration on the strength of the elephant, strength is attained. [3:25]
NOTE. Strength normally is related to muscle size and muscle amount, sinews, tendons, bone structures, and so on. The strength talked of in this case appears to be of a taller kind.
In Patanjali's book, dharana is described after the first external five steps of his system. [3:1]
NOTE. What truly helps, is meditation, which is placed as the seventh step of eight in Patanjali's system. Meditation does not depend much on preliminaries of Patanjali. They may, however, help adjustments as time goes by. "First things first" is the idea. Transcendental Meditation, TM.
In the background of Kaivalya ("aloofness") notions arise. [4:26]
NOTE. In Samkhya Yoga, kaivalya is presented as 'aloneness' and the end goal of yoga. But here we are informed that something goes on in the background of such "aloneness". At least it means that "aloneness alone" is not the end goal, then, contrary to what Lahiri's disciple, Yukteswar, teaches.
Continuously looking at one Star like a fool is called samadhi (variously described as a state of union, or of deep, inner attunement). [1:1]
The tranquil state can be attained even by the means of dreams and drowsy feelings. [1:37-38]
There are eight steps in Patanjali's Yoga: yama (restraint) is one half of one of the steps: The following points constitute yama: Ahimsa (non-violence); Satya (truth); asteya (non-stealing); brahmacharaya (celibacy, or restraining the senses to hold onto the Self); and aparigraha (not accepting help from others). [2:29-30]
NOTE. The Sanskrit terms carry many meanings and nuances of meaning too. A fresh look at what the words mean according to the SDSS (Sanskrit Dictionary of Spoken Sanskrit) might amount to help us somewhat:
Ahimsa is translated as "harmlessness; security; nonviolence; non-injury; safeness." Hence, "harmless security" might be wise to go for, and also "non-risky (safe) nonviolence" if you can do it without getting in harm's way.
Satya means such as "being genuine, sincere, valid, real, honest, truthful; sincerity; goodness or purity or knowledge." "Being truthful" is what is called for.
Brahmacharya includes Veda-study. The Upanishads, Brahma Sutras, Rigveda, and the Bhagavad Gita are of the Veda. Or the meaning is learnt to be "chastity; continence and chastity." The Veda study might be a lot of what is originally meant. The regulated life-stage might be secondary to it.
Aparigraha includes: "destitute of possession; destitute of attendants or of a wife; renunciation; renouncing; poverty; deprivation." Being poor and deprived and mateless might be allied with the ancient renunciant lifestyle of a sannyasi (wandering monk). However, general conditions in many countries are far from ideal for it today.
Yajnavalkya Yoga and a couple of Upanishads lists ten yamas. The first four of them have the same Sanskrit names as the yamas in Patanjali, but Aparigraha is not in those lists.
Due to the expansion of heart into another's body, the yogi can enter another's body, and the senses follow the mind. [3:39]
When these three - meditation, careful focus, and deep-going attunement - are unified and well mastered this is called sanyama, or "good focus". [3:4]
Four kinds of samadhi or Self-attunements include "the seed of the intellect". [1:46]
Having yogic powers may soon become obstructions to attaining samadhi, Self-attunement, although they are effective in bringing fruits to the practical life. [3:38] ◇
The other half of the step is called niyama (rule): Saucha (external purity); santosh (internal purity); tapa (that which can be known personally from the Guru); swadhyaya (listening to the sound of Om); and pranidhana (holding onto the Self). [2: 32]
To remove doubts about yama and niyama, cultivating good sentiments is necessary. [2:33]
By concentration on the lumbar center, knowledge of the physical body is achieved. [3:30]
2. One may experience doubts and certainties manifesting from the state of Realisation
In any state other than samadhi, the Self is experienced according to the waves of the heart. There are five kinds of vrittis, or "deep mind waves (or stirs)," and they are centered around attachment due to pleasure and detachment due to suffering. [1:4-5]
The following [qualities may be] attained: handsomeness, loveliness, strength and the power for bearing hardship. [3:47]
To remove doubts, focus on Venus. [* [cf. 2:33 and 3:34]
By focusing on Venus, obstructions may become fruits somehow. [* [cf. 3:34 and 3:38]
Absolute knowledge and all relative knowledge are due to inner Realization. [3:55] ◇
By concentration on Venus, all knowledge is attained. [3:34]
3. It helps to practice for major benefits as undisturbedly as can be
Remain steadfast to the great, help-offering universals in life [as long and as fast as you can]. [cf. 2:31] (5)
By focus on "character, definition and different states", knowledge of the past and future is attained. [3:16]
By concentration on the relation between the body and the sky, the body becomes as light as cotton and moves in the sky. [3:43]
When the attachments of the heart are transcended, then the transcendental state is attained. [3:6]
To remove suffering and to attain samadhi (union), kriya koga [can] be practiced. And gradually, some "inner sound," is heard. Afterwards, the supreme Being and inner wisdom are both attained. [2:2]
The radiant Self is not seen by ordinary eyes. [4:18]
When the seeker continuously and undistractedly holds onto a fit focal place for one's Self) this is called dhyana, or "meditation". [3:2]
By santosh, or "contentment," a great deal of happiness is achieved. [2:42] ◇
When inhaling and exhaling naturally stop, then pranayama is held. [2:49]
Whoever masters this concentration becomes poised in the inner Light of Wisdom. Whenever he concentrates, he will receive inner wisdom, that is, inner Realization. [3:5]
Pranayama is derived from prana ("Life Force") and ayama ("expansion"). The expansion of Life Force in the state of Tranquil Breath is the state of pranayama. [2:55]
NOTE. 'Ayama' means such as length, extension, length, and restraint. Thus: "prana-extension" along with "prana-control" or "prana mastery" and the like. A related understanding is "yoga trance induced by stopped breathing" (!). and still other understandings of 'ayama' are found too, such as non-restraint; indulgence. If these understandings are tidily applied, you may end up with something like "sweet indulgences" related to one's life" too - and that is indeed a key to non-ascetic tantric yoga.
By holding onto the Kutastha with efforts to keep the mind tranquil, can one stop those waves of the heart. [1:12-13]
When Satya, or "Truth" [Satya also means integrity] is established, then Kriya becomes fruitful. [2:36]
The Seer is Consciousness only. -- The Atom of Brahman, or "the ultimate Self", is beyond objects. [2:20; 1:36]
NOTE. It consciousness only sees the "atom of Brahma", beyond "things", it means your core is not a thing, not something physical, and only is discernible by subtle consciousness. ◇◇
The inner Self is beyond time. [1:13]
NOTE. It means your core may discern past and future things too.
Dhyana, Dharana and Samadhi - meditation, a focus, and Deep-Self-attunement - are of the inner side and external to the state beyond the inner Sound that is called Omkara (Om, Aum). [3:7-8]
Many say they gain in Self-awareness and Being by meditation. It may be wise to practice meticulous sanyama (intense yet lax focus in deep meditation) along with meditation with the aim of gaining yet more yoga benefits as Patanjali goes into.