Just as building a foundation is an absolute necessary phase to building any structure, the most important aspect of the construction of the spiritual edifice of yoga is constituted by the moral and ethical practices called Yamas and Niyamas.
For the majority of aspirants, the main focus of their sadhana should be the development of yama and niyama. More advanced practices such as meditation should also be pursued, but one must understand that no substantial progress will take place until the 10 practices of yama and niyama are tangibly established.
The Five Yamas
It should be noted that all yamas should be practiced in the spirit and by the letter. Furthermore they should be applied in deeds and words, as well as thoughts. Perfection in any of them is for the very few but much progress can be made in a given lifetime. Also they should each be practiced in relation to each other. Sometimes they will seem to conflict and much soul searching will be needed to know how to act righteously. For example: telling the truth may harm people.
Ahimsa, or non-injury and implies non-killing. More comprehensively, ahimsa means "entire abstinence from causing any pain or harm whatsover to any living creature, either by thought, word or deed. Non-injury needs a harmless mind, mouth, and hand. Ahimsa is not mere negative non injuring. It is positive cosmic love.
Satya is truthfulness. It is more than just telling the truth. One's actions should be in accordance with one's words and thoughts. God and man's true self are truth, and in order to tune in with that consciousness we need to live truthfully at all times. Furthermore lying creates many thoughts in the mind which go against the yoga objective of calming the mind.
Brahmacharya has two main meanings. In the broad sense it means control of the senses (indriyas). More specifically, it refers to celibacy or chastity. Like all traditional spiritual traditions, yoga advocates restraining from indulging in sensual gratification. One of the many reasons is that practicing the higher limbs of asthanga yoga- dharana, dhyana, and samadhi require a tremendous amount of energy or prana. This energy is built up through the practices of yoga such as asanas, pranayama, and japa (meditative chanting of mantras) but is dissipated during sensual enjoyment. Of all the sensual activities, sex is the one that will be the most depleting to the psychic and nervous system. Most people don't like to hear this but, like the other yamas, everyone should practice brahmacharya to the best of their ability. It is a fact that the more people gratify their senses, the less energy they have and the less ability they have to meditate om thr absolute.
Asteya is non-stealing. This one is pretty self explanatory. However, it is good to bear in mind that there are many subtle ways to appropriate what does not belong to us. As for the other yamas, much self-analysis will be necessary to catch the subtle lower tendencies or our mind.
Aparigraha is non-covetousness (cravings for possessions). This involves being happy and content with what we need and not always coveting unnecessary and luxury items. To possess more than we need is a violation of this percept. Note that aparigraha includes the notion of not accepting gifts that would blind us to the giver.