It really depends whether you are playing open stance or closed stance.
If you are right handed and are playing a FH you will have your right leg outside on the open stance and your left leg across on a closed stance.
On the BH the left leg is outside on the open stance and the right leg is across on the closed stance.
My personal coaching preference is def open on the FH and closed on the BH for short balls with the option of going open on deep balls.
Check out www.powertennistraining.com
for footwork drills etc that will make your shots more effective.