lightly take a file to the widest part of your board, and move around the nose and tail doing so. If your primarily doing rails, you can lightly detune 3-5 inches inside your binding. You dont want to detune the whole area between your bindings, just the most likely spot that a boardslide will land.
You don't have to detune at all if you dont want to, but the nose and tail detune will give you better turn initiation and release. And makes riding flat base easier cause the boards will be less catchy.