There are quite a few different ideas for hitting a fade (a shot that curves left to right for right-handed players) and a draw (curves right to left). But one of the simplest ways is to control the movement of your shoulders through impact.
If you want to play a fade, your right shoulder should work down and under. Think of your shoulders rotating vertically, like a Ferris wheel. That helps hold the face slightly open at impact (above, left) -- setting up a curve to the right.
If you want to hit a draw, your right shoulder should stay high and rotate around toward the target. Think of your shoulders rotating horizontally, like a merry-go-round. That encourages the face to close at impact (above, right) -- setting up a curve to the left.
David Leadbetter is a Golf Digest Teaching Professional and is based at ChampionsGate near Orlando. He operates 26 golf academies worldwide.