Technically, the qualifications aren't many. If the people vote you in, you're President. And the people are an unpredictable (sometimes largely misguided) bunch.
You do have to be a natural-born citizen (yes, Hawaii counts), you need to be at least 35 years old, and you have to have been a resident in the U.S. for at least the past 14. Aside from that, a long, successful career in politics bodes well for you, although we're getting closer and closer to electing some charismatic, activist film star to office. You're also going to want to have boatloads and boatloads of money, or at least be tight with others who do, because this getting-elected-President thing isn't cheap.