Reams and reams of golf literature has been written on ball position in relation to your stance. The predominate theory is to have the short irons farthest back of center and to move forward towards the forward foot as the length of the club gets longer. I have a series of pictures that I hope will better explain where I recommend you start out with your ball position. Remember though, everyone is different and you may need to adjust to your swing to get the optimal ball strike.

Lofted Wedge

Set the ball farthest back on the shortest irons. This helps inhitting the ball first and due to the shorter swing arc of the shorter clubs, the best impact position is farthest back in the stance. Remember, the goal is to hit the ball first and turf second. As you can see, it is actually behind the center of the stance.

Here is the driver.

I have to work on getting it even farther forward as I like to see the woods played off the forward heel or even the forward toe. If you suddenly start hitting the ball differently than normal, check your ball position FIRST! This ball faded since the club has the widest swing arc and could not get back to square at impact. A long layoff from playing, such as over the winter, can easily make you think the ball is where you want it when it is not.