Of all the restrictive rules, that relating to the taking of sattvic food in moderate quantities is the best; by observing this rule, the sattvic quality of mind will increase, and that will be helpful to Self-enquiry.

~ Ramana Maharshi
   [Who Am I?]

Before studying anything else one has to study the Self. One has to study one's physical body, and one's subtle body and look within to the causal body. There is nothing else to study so no line of study is prescribed. Whatever may be useful according to place and time, and the type of literature which pleases you or seems to satisfy you, you can get help from them. It can come from any source, it makes no difference. The emphasis is the Self and the non-self. One has to study the Self so as to separate the non-self - one has to experience happiness so as to leave behind misery and unhappiness. One has to find what is useful to the True Self and make use of it and discard what is not useful to the True Self. These are the ways one can study.

~ Śāntānanda Sarasvatī

A silly idea is current that good people do not know what temptation means. This is an obvious lie. Only those who try to resist temptation know how strong it is.... A man who gives in to temptation after five minutes simply does not know what it would have been like an hour later. That is why bad people, in one sense, know very little about badness. They have lived a sheltered life by always giving in.

~ C. S. Lewis