The problem is that the reasons that caused a breakup are not always very clear. Usually women are not able to determine the reason they are feeling the way they are, because they become more emotional than men.  Spending too much time to find the causes of the breakup is not a smart use of the time.

The first move after the breakup should be to stop thinking about the relationship for a certain period of time, like one or two months, trying to focus on your personal life.  Going out and making new friends will help you.

After that period of no communication with your ex girlfriend, you need to play strategically. Begging her to come back with you is not a good idea.

Showing your ex that you are doing well without her is a smart move. She is probably missing you as much as you are, and that behaviour will make her think again about the relationship. You must not overdo that situation, making her jealous dating another girls to show you are doing great without her.

The key point is to try not be too emotional, take things calm and you will be in the way to get your ex girlfriend back.