Honestly recognize why you need to interest girls. Maybe it's just the memories came flooding back, but you are so different, that it is not worth trying?! If any important parts you do not like, do not think that the second time something will change.
Understand why interest is lost. Knowing the cause, you can be sure. And if you understand the arguments for girls is difficult then ask for help for her friends – they can help you understand your favorite.
Remember who was the initiator of the break. This will significantly affect your future actions. If you dumped her, then you need to wait a while before acting – there's too much chance that she's holding a grudge, and possibly pissed at you. If it broke, then two options: either you are not very satisfied, or she found someone else. In any case, you must be willing (if you need) to adapt to it and to please. She needs to see that you are not the same as before.
Start from afar. In order to find the "ground", you need to check how it reacts to you. Send her a message or a letter, call or intersect by chance, but all the affected threads must be neutral and does not apply to your relationship. So you gradually come into her life again.
Try to become a friend. In the full sense of the word – just a friend without sex. If necessary, and girlfriend. She needs to feel so comfortable with you to begin to complain about the vicissitudes of life, to discuss the guys she likes and her friends, the lead in a difficult situation. In short, become everything to her – support.
Use that knowledge. Remember that the advantage is on your side. You know what she likes and what not. How to react to different situations, what is going crazy. If skillfully direct this information into action, you will be able to win her heart. Why should she waste time on a man who doesn't understand when there's you?!
Discuss the situation. Sooner or later it will have to do. Apologize for past mistakes and offer to try again.