Sometimes we can find ourselves fixating on the past. The best thing about the past, however, is that it is over. That time has come and gone and you are not there anymore. Put it behind you and focus on today and your future. Don't let the past control your present. When you find yourself fixating on the past you can try these exercises:
1) Do something to distract your mind, physical or mental, and disrupt your thoughts. This can be as simple as going for a jog or asking yourself some questions like, "What noises can I hear right now?" or "If I could eat anything in the world, what would it be?" The value in this is to move your mind away from upsetting thoughts and redirecting them to something specific and tangible.
2) Learn to understand your triggers and your thought patterns. Do you fixate on the past when you are feeling vulnerable? When you are feeling anxious? Do you constantly ruminate about a mistake you made? The next time you start to fixate on the past or ruminate on the could haves, should haves, would haves, say to yourself, "I am aware of this pattern, I know that I can't change what happened, that event is over now. I have moved on."
3) Leading on from that, learn to distinguish between helpful thoughts and avoidance. Occasionally, reflecting on the past gives us useful insights and can teach us things about ourselves and others. The more you fixate, however, the less useful these thoughts become and can affect your overall problem-solving skills. When you think about the past or a mistake you have made, think of solutions instead and act on them straight away if you can. Ask yourself, "What is the best choice I can make right now?" It might be as simple as, "let it go and move on," or it might be, "fix that mistake." Either way, you are switching your thinking to problem-solving 
