Don't talk to her for a few days.
Girls need time to think, she'll eventually recontact you or if not you can do it after a day or two.
Keep in mind that not talking to her is not the same as ignoring, you can reply to her if she engages in conversation with you. It's crucial that you let the ball be in her court for those first 48-72 hours of the breakup.
The logical step during this time is to do a self evaluation: What happened to cause the break up? What lengths are you willing to go for her? What kind of chance do you think you have?
Using this information, you should be ready to talk to her once the first few days are up and she's calmer.
You can split up the task into multiple sections:
For instance, girls enjoy reminiscing on greater times so you can do your best to bring up old memories. Be sure not to sound too sappy, strive to remain as confident as ever.
To elaborate on this, pity will get you nowhere. If you show her you're hurt, the ball will be in her court for longer than you're going to want. You eventually want to control the conversations, and how they end. The best thing to do with a girl is slowly ramp up the conversation and then finish it with one hard hitting question for her to sit on for that night.
Do this for a few days, then talk to me.