Allah Ta’ala states in the Qur’aan Majeed:
"Verily, virtuous deeds eliminate evil deeds."
The evil deeds mentioned in this aayat refer to Sagheerah (minor) sins. After a minor sin, if a good deed is done, the sin is eliminated. It is therefore essential to always render deeds of virtue so that the numerous sins we commit are eliminated. Even after Kabaa-ir (major sins) have been committed, virtuous deeds should be done in addition to Taubah (repenting).
http://www.themajlis.net/QA.html