When trying to fix your pull, the best strategy is to encourage the exact opposite fault; a push. Unfortunately, after awhile practicing the same incorrect move over and over again, it will begin to feel comfortable in your swing.
To really understand how to perform the correct motion, you need to feel the opposite of the incorrect move you are performing. This drill is designed to encourage a push. With some practice you will find the happy medium between your pull and the newly created push.
This drill is difficult to setup, but very effective once you get it going. Take a look at the enclosed pictures, and try to setup your shafts the same way. Explaining what I did here in words would be pretty much impossible. The keys are having the shaft closest to you parallel to your club at address. Also making sure that the far shaft is slightly farther away from the hole, as this will encourage the in to out swing path we are hoping for. Also make sure there is enough room for error between the shafts to make decent contact with the ball.
Remember that hitting the shafts can be dangerous, so take this drill slow in the beginning.
Setup normally to the ball in the center of the shafts; notice how the shafts will force you to swing on an in to out path to make contact with the ball. Definitely start by swinging slowly, and consider starting without a ball. The idea is to hit the ball and miss the shafts entirely. You should notice immediately how different the swing path feels. It should feel like your going to hit yourself on your backswing. Try this drill for ten swings, then step away and try hitting balls normally. If you’re still pulling, try the drill again.