Well, the first thing you do is grab a times guide at the park and figure out where the Princes are going to be and at what time.
1. Wait your turn in line.
2. Ask him nicely. It helps if you're a little nervous.
3. Ask his princess nicely.
4. Smile pretty! Make sure the photographer takes two photos, in case one doesn't turn out.
You can always give your personal camera to the Photopass photographer.
The one Prince I missed? Snow White's Prince. He refused 3 times at Mickey's Not-So-Scary Halloween party, even after Snow White said she loved the idea. Harumph.