You build on failure. You use it as a stepping stone. Close the door on the past. You don't try to forget the mistakes, but you don't dwell on it. You don't let it have any of your energy, or any of your time, or any of your space.
“May I make a suggestion, hoping it is not an impertinence? Write it down: write down what you feel. It is sometimes a wonderful help in misery.”