early game you have to farm it up and stay cool and a trick is to hit a minion with a rocket when a champion is near it you will get harrase without minion agro and after you get a couple of items you can fight try loking down a target
late game you are very strong stay in the back lines with your Q on rocket launcher it shuld give you a 700 range at full rank witch is equal to a turret and try to hit the closest target if someone is trying to get you alone switch to your minigun and kill him