Take several photos.
One of the first things I learned in my journalism photography classes was to take way more pictures than you need. Chances are, out of the 20 or 30 that you’ve taken (assuming if you’ve taken that many), at least one of them will turn out pretty good. And, you can always delete them later on.
And, here’s a tip for all of you iPhone users out there: if you hold down the center button in the camera feature, you can take a “burst” of photos. Using this will help create a library of photos to choose from, and you can pick and choose what came out okay — and what didn’t.