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If you're doing better than your teammates, don't be afraid to take charge. You'll be most of the damage, so they should probably follow you.
If you're doing worse than your teammates, try to be useful and just don't die. It's better to be unnoticed and win instead of trying to be a hero and having 4 people rage at you.
If you lose a few games in a row, play a blind match or take a break. Usually it'll make you feel better.