Rub and massage it thoroughly or move it around even though it's numb. You can still move it, but you won't feel it while moving it and that should get the blood pumping and flowing back through it. I hate when that happens because I'm afraid I'll end up breaking my foot or ankle since it's numb and I wouldn't be able to tell or feel until it stopped. -____-
Say, "Wake up little guy! It's time for school." Make sure you have a lot of enthusiasm in your voice. You know, if you set your foot on the ground, relax it, and keep it perfectly still, you won't feel anything. But if it moves or gets touched, you'll feel a quick stab of tickling. Keep it as still as you possibly can, and the pain will eventually subside.
Age old remedy - and it works. Pinch your earlobe of the opposite ear i.e. left ear if your right foot is asleep. Hold it for a few seconds. You will immediately feel your foot getting back to normal. Hold until it is completely awake.