The first limb of yoga is the Yamas, which are the guideposts for how to behave in society. The Yamas describe how to treat others and how to treat yourself.
Ahimsa is non-violence
The word Ahimsa, literally means to not injure, or show cruelty to any creature or person.
This Yama is the first for a reason. For all the other Yamas and Niyamas need to be carried out with Ahimsa in mind.
Satya is truthfulness
Satya means to speak the truth, but is not limited to the spoken word only. It implies truth in all action.
Asteya is non-stealing
Asteya means to to take nothing that is not rightfully yours to take.
Aparigraha is non-covetousness
Aparigraha means to take only what is necessary. This includes not taking advantage of any situation.
Brahmacharya is abstinence
Brahmacharya means abstinence, most particularly in regards to sexual relationships. This is not meant to be a forced repression of the sex drive. It is meant to transform the sex energy into fuel for the journey to higher consciousness.