I think an important part of successful people is that they have learned to accept the fact that what is in the past is finished so they can fully dedicate their time to the present and future. I know a lot of my time is eaten away my regret when I'm particularly down. But regretting things often doesn't help and so the best option is to not let your past mistakes stop your future self. It's definitely tough but the most important part is to change the way you think. I know a lot of people find it useful to repeat affirmations to themselves. But the rest is really just practice in situations. It takes a long time but building self-esteem and acceptance for who you are is one of the best things you can do for yourself. And with that will come hope and motivation.

Best of luck!