It's usually easiest to let go when you have something new to hold onto. Try making new memories, finding a new hobby, or doing something different with your life.
Accept the fact that what is done is done. You cannot go back and change what has happened. The only productive way to move on is admit and learn from your mistakes.
Accept the past and set yourself a limit for mourning it. When a person keeps telling herself "forget that, move on", that just makes it a constant present.
