Stop assigning blame. This is the first step. Stop assigning blame and leave the past behind you.
You know whose fault it is that your life isn't perfect. Your boss. Your teachers. Your ex-lovers. The ones who hurt you, the ones who abused you, the ones who left you bleeding. Or even yourself. You know whose fault it is — you've been telling yourself your whole life. Knowing whose fault it is that your life sucks is an excellent way to absolve yourself of any responsibility for taking your life into your own hands.
Forget about it. Let it go. The past isn't real. “That was in another country, and besides, the wench is dead.” If we're not talking about something that is real and present and in your life right now, then it doesn't matter. Nothing can be done about it. If nothing can be done about it, then don't spend your energy dwelling on it — you have other things to do.
I may sound cruel, I may sound simplistic, I may sound like I'm saying you should just “get over it,” by suggesting that you should let go of your past. I'm sorry for that. But life won't hold still and wait for you to lick your wounds. The race is still being run. Get up and keep moving. You can't do anything about yesterday.
You can do something about tomorrow. And about the next day. Focus your energies there.