John P hit the nail on the head. But I want to re-emphasize "light coats" When you apply light coats it will not look great at first, it will be a bit cloudy, and the tendency is to keep applying it until you see a sheen. That is wrong, just apply one light coat, which will look hazy/cloudy, but it will self-level and clear up in an hour or two. I usually use two or three coats of future, depending on the type of paint I am clear coating.
I wait 24 hours in between future coats, and a full 48 hours after the last coat of future before applying decals/washes/pastels so the future is fully cured.