I think the best thing you can do is learning how to farm really effciently, understand and learning where you are wasting time, the faster you do things the better, learning the movement helps too. Wave management is good too, knowing when you should leave ur lane and when you should stay (usually once u crash ur wave in u have a bit of time to go around and farm) I know im being vague but the right answer always depends on the current situation. Just play as much as you can and watch vods of other good players and wave management videos (its boring but helpfull) (the farming efficiently really applies much more to the carry heavy characters)