Sometimes it's hard to know the best ball position for a given shot. While there are many general rules that can help – for example, the best ball position for an average shot is somewhere between your left armpit and the center of your chest (for a right-handed golfer) – there are ways to find the ball position that gives you the best results for the way you swing.
The Correct Position
The "correct ball position" isn't the lowest point in your swing arc. Rather, there are two different definitions. If the ball is on a tee and you're hitting a driver, the ball is usually placed just inside your left heel (for a right-hander) and high enough so half the ball is above the top of the driver. That's because you want to hit your drive with an upward swing. But for other shots – with the ball on the ground – the correct ball position is about 1 inch behind the spot where you hit the ground and take a divot.
The Middle of Your Stance
The middle of your stance is usually a good ball position for most shots off level ground. To find it, place a club on the ground between your legs. The butt of the club grip should point at the ball. Straddle the club with both feet parallel to the shaft; the ball will appear to be centered between your feet. Fan your left foot outward, toward the target. The ball now appears to be farther back in your stance, but it's actually centered between your heels. This is the actual middle of your stance. As the club gets longer, the ball should be moved forward from this position. But unless you're a very skilled player, you'll rarely need to move the ball more than 2 or 3 inches ahead of the middle.
The Bottom of Your Arc
The normal swing of most players will hit the ground an inch or so past the middle of their stance, closer to the left foot. But if you want to find out exactly where your swing hits the ground -- or if the ground is uneven and the center of your stance isn't a good gauge of where the club will strike the ball -- you can find where the bottom of your swing arc actually is. Just take your address position without the ball and make several swings. Let the club hit the ground each time. The spot where your club hits the ground most often is where the bottom of your swing is. Note this position, then set up with the ball about 1 inch behind this spot.
When you're faced with an awkward shot, you may have to hit the ball from an unusual setup position. The best you can do is a variation of the method for finding the bottom of your arc. Take an address position as similar as possible to the one you'll actually use. Grip the club in whatever way the shot requires, and take some practice swings. Note where the club hits the ground, then set up so the ball is about an inch behind that position.