A good swing starts with a good grip. A bad swing starts with a bad grip. Because most amateurs fail to put their hands on the club properly, they'll never be able to play as well as they should.
I use the Vardon overlapping grip. I feel it unifies the hands and promotes better wrist hinging. My left hand goes on first, and I turn it to see two knuckles (below). My left thumb rests just right of center on the shaft.
I like those molded practice grips for learning how to hold the club. The grooves will put your hands in the correct positions. Even though it makes the clubhead feel too light, I suggest you get one and hit balls with it to improve your grip.
The mistake I see most is a grip that's too weak. People put their thumbs straight down the shaft, and the result is usually an open clubface at impact--and a shot that peels off to the right.
A grip that's too strong, where you see too many knuckles, will likely cause the clubface to be closed at impact. It's a power grip, especially if you're a slicer. Still, I'd rather see your grip too strong than too weak.
MORE THOUGHTS FROM TOM
Bubba's Masters victory was a welcome surprise. I practiced chipping near him early in the week, and to my ear he was hitting every shot absolutely dead solid. I watched him and realized my hands weren't quite far enough forward. It helped my game.
Tom Watson is a Golf Digest Playing Editor and the golf professional emeritus at The Greenbrier, in White Sulphur Springs, W.Va.