I use this theory: -

put feet together with the middle in line with the ball. I move my left foot about 2 - 2 1/2 inches to the left and my right foot just past my shoulder width for a driver or 3 wood, for mid irons /hybrids I move my right foot to shoulder width, for wedges/high irons I move my right foot about 2 - 2 1/2 inches to the right as with the left.

I find playing my driver off my left heal too much for me, so I sit it in line with the badge on my shirt usually.