As described in Chapter XVI & XVII of “Shri Sai Satcharita”, Sai Baba gave a rather long discourse on the subject, the purport of which is given below:
Qualifications for Brahma-gnyan or Self-realization
All persons do not see or realize the Brahma in their life time. Certain qualifications are absolutely necessary.
1. Mumukshu or intense desire to get free. He who thinks that, he is bound and that, he should get free from bondage and works earnestly and resolutely to that end and does not care for any other thing, is qualified for spiritual life.
2. Virakti or a feeling of non-attachment with the things of this world and the next. Unless a man feels disgusted with the things, emoluments and honours, which his actions would bring in this world and the next, he has no right to enter into the spiritual realm.
3. Antarmukha (introversion) Our senses have been created by God with a tendency to move outward and so, man always looks outward and not inward. He, who wants self-realization and immortal life, must turn his gaze inwards and look to his inner self.
4. Catharsis (eliminating all base ideas and emotions)-Unless a man has turned away from wickedness and stopped from doing wrong, and has entirely composed himself, and unless his mind is at rest, he can not gain self-realization even by means of knowledge.
5. Right conduct-Unless a man leads a life of truth, penance and insight, a life of celibacy, he can not get God-realization.
6. Preferring Shreyas (the good), to Preyas (the pleasant)-there are two sorts of things viz. the good and the pleasant; the former deals with spiritual affairs, and the latter with mundane matters. Both these are open to man for acceptance. He has to think and choose one of them. The wise man prefers the good to the pleasant, but the unwise through greed and attachment chooses the pleasant.
7. Control of the mind and the senses-The body is the chariot and the self is its master, intellect is the charioteer and the mind is the reins, the senses are the horses and sense-objects are their paths. He who has no understanding and whose mind is unrestrained, has his senses unmanageable like the stray horse of a charioteer does not reach his destination (get self realization), but goes through the round of births and deaths; but he who has understanding and whose mind is restrained, has his senses under control, like the good obedient horse of a charioteer, reaches the destination, i.e. the state of self realization, whence he is not born again. The man, who has understanding as his charioteer (guide) and is able to rein his mind, reaches the end of the journey, which is the supreme abode of the all-pervading, Vishnu (Lord).
8. Purification of the mind-Unless a man discharges satisfactorily and dis-interestedly the duties of his station in life, his mind will not be purified and unless his mind is purified he can not get self-realization. It is only in the purified mind that, Vivek (dis-attachment to the unreal) crop up lead on to self-realization. Unless egoism is dropped, avarice got rid of and the mind made desire less (pure), self-realization is not possible. The idea that “I am the body” is a great delusion and attachment to this idea is the cause of bondage. Leave off this idea and attachment therefore if you want to reach the goal of self-realization.
9. The necessity of a Guru-The knowledge of the self is so subtle and mystic that, no one can by his own individual effort ever hope to attain. So the help of another person-teacher, who has himself got self-realization, is absolutely necessary. What others can not give with great efforts and pains can be easily gained with the help of such a teacher, for he has walked on the path himself and can easily take the disciple step by step on the ladder of spiritual progress.
10. And lastly, grace of the Lord is the most essential thing. When the Lord is pleased with anybody, He gives him Viveka and Vairagya and takes him safe beyond the mundane existence.”The Self can not be gained by the study of Vedas, nor by intellect, nor by learning. He whom the self chooses gains it. To him the Self reveals its nature” says the Katha Upanishad.

Om Samartha Sad Guru Sai Nath Maharaj Ki Jai.