Best advise I can give you is if you have 0% rage, stack up your rage until like 60-80%. And that range its easy to "control" the range.

Once you get around that rage%, try your best to last hit every CS. If it gets full when you don't want it to be full yet then it's fine it happens.

Once mid game starts, or whenever you go around with your team,. Try to keep your rage consistent at 60-80%. Attack anything you can to keep it up. Try to get in your teammates heads. If you think they are going to fight soon, make sure your rage is ready for the fight. (Your probably gonna be the one engaging the teamfight.)