For most golfers shaping the ball in the air happens accident but for the game's better players it used to get the ball closer to the hole or hit a fairway. In this video, Justin Rose explains what he does to shape the ball both ways.
Start Line Versus Target Line
To understand how to shape the ball it is important to understand the difference between a target line and a start line. The target line is a straight line from your ball to your target. The start line is the line that you want the ball to take off on, so left of the target for a fade (right-handed) and right of target for a draw.
How To Hit A Fade
To shape the ball left-to-right (for right handers), you want to see the clubface on the target line aimed straight at the hole, but aim your feet and body on the start line, left of the target. Once you are set-up in that manner, you want to focus on, and swing along, your start line. Doing this will get the ball starting left, but with the clubface pointing at the target the ball should shape back to the right in the air.
How To Hit A Draw
To hit a draw (right handed), you want to follow the same method but with the start line facing right of the target. Keep the clubface pointed to on the target line and then swing along the start line. This will get the ball starting out to the right of the target, but shaping back in the air.