Jim McLean. Now, his decades of experience are distilled into 120 drills that will help every aspect of your game in Golf Digest's Ultimate Drill Book.
The book covers the complete game from stance, grip, alignment, and posture to the full swing with every club from driver to putter. McLean also has some excellent drills to build your stamina and flexibility as well as a few to sharpen your mental game--something many instructors talk about but only a few, like McLean, offer any practical help with. All the drills are described in a four-part format: Problem, Result, Goal, and Practice Procedure. There are plenty of annotated photos to illustrate each one.
I recognized several of the drills from the time I spent at McLean's school at the Doral, but I also found many fresh ones, too. One of my favorites is the Right-Arm-Only On-Center Drill, which teaches how to co-ordinate body and arm action. It's also one (of several) you can do on the tee while you're awaiting your turn to hit. I also particularly like the Pacific Ocean Drill, where the player imagines hitting balls at a target the size of the ocean in order to encourage a free swing unencumbered by attempts to steer the ball.
McLean is one of the game's greatest teachers. You may not be able to make it to one of his schools, but you can benefit from his wisdom with this simple, thorough instruction book.
Among many other books, Dave Donelson is the author of Weird Golf: 18 tales of fantastic, horrific, scientifically impossible, and morally reprehensible golf