I always make my belt snug to the point of it you can push up on it from the bottom and get about 3/4 of a fingertip in play with it, you're good. If you go too tight the belt will snap almost immediately, guaranteed.
If you go looser than that, the belt will last longer, but you're going to slip all the time and not get any good PSI.
After 3 or 4 belts, you'll get the hang of it