Other than taking a lesson I would say the easiest drill is to get a half full waterbottle and place it just outside the ball. This will let you know if you're coming from out to in on your path. If you can miss the bottle you will be most likely hitting it pretty straight or with a slight draw. If you can't fix a fade, maybe just learn to control it. By having a go to shot you'll cut half the fairway out of play. Being predictable on the course is always a good thing.