I know is only human nature to become very emotional when you break up with the special someone. You have got to fight that urge with ever fiber of your being, otherwise it will be very tough to win back an Ex Girlfriend.
Your first tendency, right after the breakup is to go on the offense. Call her a bunch of times during a day, leave a ton of voicemails, show up at her home to profess your undying love to her.
I'm sure just reading that, you can probably get a sense of how that would come across. Now think about how that would look from your ex girlfriend's perspective. I'm sure you could imagine it wouldn't be a pretty sight.
Doing something like this will only intensify the breakup. You need to take it nice and slow. Take Your Time.
Time can be the great neutralizer in a breakup. I can guarantee that no matter which person caused the breakup, time can shoulder the blame. It releases all the anger, rage, and hostility that there may be. It lets both people relax and gather their thoughts, so every time they talk to each other it doesn't have to be a screaming match.
A HUGE benefit that time gives to you is it allows her time to miss you. You may not think that is the case right now, but all that time apart, I can almost assure you that she'll start to think more fondly of you. After all, there is a lot of history there, and those are feelings that you just can't put away.