I think what it means is that in his past he's done a lot of things he knows he shouldn't have done. And he's starting to realize it. So by saying practice makes perfect he means he's trying to become something his mother could actually be proud of.
Instead of a partier, druggie, what have you.
That's the way I look at it, & personally this song has like totally changed my view on things I've done in my own past, & helped me change for the better.