There isn't a good way. If it's too high, take the gear off and gently tap it down to seat it deeper in the bearings. Too low is tricky. I don't remember seeing one too far off from the factory, but when I replace the bearings it can happen, especially when I forget to mark where the original one was and have to guess a bit.
If the belt is frayed, it can add friction to the system. Usually it doesn't stay frayed long as it will snag on something, derail or snap.