I do the same as what Wiggy said, expect for the inside, I make sure it is slightly bigger, or I add a small border around the outside, usually black, but it depends on the color of the inside. I do this because no matter how much time you spending trying to get both centered, it never works out perfect. I always cut on the front side because I want it perfect, but the inside usually has a little bit of white (non printed) on one side that didn't line up perfectly. If you have a small border around the outside, that won't show up.
