Already comfortable with basic dribbling drills? If you need more challenging drills, consider doing ones that require two-ball at once: Dribbling-a-la-Chef-Curry
You will not be able to do many of these drills at first. Be patient and continue to work - it may take twenty minutes or more just to get 2-3 dribbles in a row. But the mental ability to track and correct two moving basketballs simultaneously will accelerate your in-game handles tremendously!
The website "Coaches Clipboard" has some great drill ideas here.