I don't really need to practice them anymore, but when I began (about your age) I spent at least and hour a day. When I would ball, I would stay and practice for 1- 2 hours. Don't just practice dribbling though, practice passing too. I used to pick a spot on a wall and pass at it. Left handed, right handed, behing the back, off the dribble, off spin moves, jump passes. Work on your whole game. Another thing to remember, footwork is a major factor in how good/effective your moves are.