There are 2 steps to hitting a draw. First, you need to change your set-up. And then you will change the way you swing a golf club.
In general, adjusting your set-up is good enough to hit a draw. But if you are a slicer, you might still have some difficulties in hitting a draw. If that's the case, I'll explain how you should swing the golf club to curve the ball from right-to-left.
1. Adjusting Your Set-up
There are 4 key points to adjust the set-up.
a. Aim right of the target.
b. Put the ball little more right than normal.
c. Position your right hand toward the inside of your left thigh.
d. Make sure your clubface is facing the target.
We are going to hit the ball from right to left. So we should aim right of the target. The more you aim right, the more you will curve the ball left.
Next, with a 7-iron, position the ball in the center or a bit left of center. Slicers tend to put the ball too far forward and cut cross the ball. To hit a draw, you need to swing from inside the target line.
Placing the ball back will help you do that. Don't forget ro position your hands in front of your left thgih. Your hands tend to return to that position at impact.
For an experiment, position your hands in front of a zipper. Now, move your hands forward. I think you will find out that the face opens as you move your hands forward. This will definitely cause a slice. Pay attention to the position of your hands.
When gripping the club, turn your clubface so that it's facing the target. After turning the clubface, you can now grip the club.
Most players grip the club and then close the face. But if you do this, the face will open on the downswing because of the centrifugal force. Make sure to close the face first and then grip it.
At address, you are aiming right of the target, but your clubface should be pointing the target.
2. Changing Your Golf Swing
If you are a slicer, adjusting your set-up might not be enough because you have all these old habits of hitting a slice. Hitting a draw is like hitting topspin forehand in tennis. Let's take some practice swings using your right hand only. We don't need a golf club for this drill. Try to pretend your right palm is your clubface.
Swing to the top. As you swing down, try to face your right palm toward the ground. At impact, it should be facing down toward the ground. Take a few practice swings with your right hand like that. Now, grip a club and try to swing with the image you got from the drill above. Start with 60% of your swing speed. Hit some balls. You should be able to hit a big draw.
Reference: http://www.golfsamurai.net/slice/how-to-hit-a-draw.htm