I am writing a story in which the characters have some power over the physical world - literally able to transform their knowledge of physics into powers. I am trying to determine a good way for them to fly. Literally anything is available to them that has some kind of physical law attached to it.
My current plan is just to say that they can choose to cancel out gravity, but I realize it means they would just start floating, not necessary moving in any particular direction. If they change the air pressure around themselves, then they'll have to do all sorts of odd things in order to not pop their eardrums and whatnot. If they create explosions by concentrating oxygen and spiking the temperature, then they're going to die from being exploded (hah).
Edit: I'd like to say that I really appreciate everyone's input on this question and I hope it helps other people playing with such a world. I accepted the answer that worked best for me, but there's still plenty of great answers in here! Please upvote everyone, they deserve it.