Then is over; this is now. The less time and effort you put into looking at the past, the more you will have for living and experiencing this day. You will also find that letting go of the past will give you a deeper sense of strength. Instead of allowing past mistakes and worries to drain your energies, you will have a renewed energy to live your life to the fullest and enjoy it more.
Being content with yourself and optimistic about your future is not difficult. Whatever is in the past is over; learn from it and move on. When you are self-motivated enough to do this, you will see that moving ahead is the best definition of living life.
With that said, what can you do now? Sure it is easy for me to tell you to forget the past, yet it is a whole different practice to actually do it. Life is a complex set of events much of which of course is real, yet a large amount is just your view of what really happened.