One of the biggest footwork mistakes that tennis players make is using the incorrect footwork stance to hit the ball. Using the incorrect stance means using a stance that doesn't allow you to rotate or maintain your balance during contact. In the picture you see above the stance that I'm about to use will prevent me from rotating and because of this my hips will lock out the rest of my swing. Whenever you lock out your swing it will also lock out the amount of power that you can generate from the stroke.
What you want to do is select a stance that will allow your hips to rotate open so you will not lose power from your swing. In the picture above I'm using a open stance that allows my hips, shoulders and racquet to rotate completely which means I can generate more power using this stance in this situation then the previous stance shown.
Summary of the Mistake Footwork mistakes video: