I've read a few ahadith etc.. that say that when you sin you should do repent and then do good deeds

now..ive wondering what sort of "good deeds" you should do, are they the one that benefit only you, or do you have to do something for someone else or???

like reading the Qur'an, or reading an islamic book? are those the "good deeds" mentionned in the ahadiths?

btw..here im talking about sins that will only hurt yourself (like missing a prayer without a valid excuse etc... NOT sins like backbiting or hitting someone, which involve someone else and which you have to ask forgiveness to the person before asking forgiveness to Allah)