Avoid the 7 great destructive sins. The Muslims enquired, “O Messenger of Allah! What are they?". He said, “To join others in worship along with Allah (shirk), to practice sorcery (magic), to kill the life which Allah has forbidden except for a just cause (according to Islamic law/murder), to eat up Ribah (usury/interest), to eat up an orphan’s wealth (usurp), to give back to the enemy and fleeing from the battlefield at the time of fighting (cowardice), and to accuse chaste women, who has never thought of anything touching her chastity and are good believers (false accusation).” 

(Hadith Bukhari, Wasayah, 23; Tıbb (Medicine), 48; Muslim, Iman (Faith), 144)