My guitars knobs have been rattling around lately. They still work and everything but I was just wondering how to tighten them. I took the back panel off but I don't know what to do from there.

The guitar is an ESP M-50 if that helps.

Sorry if this topic is in the wrong spot and thanks in advance.
Pop the knob off the front of the guitar, then tighten the nut, whilst holding the base of the pot inside the control cavity. The nut is 8, 10, or 11mm.. I can't remember which. If you don't have the right socket size, just use some pliers, but be CAREFUL. It's easy to slip, then mash the nut and your guitar's finish.
If you have trouble getting the knob(s), just use a flat bladed screwdriver to give you a bit of leverage. Again, be careful though, because one slip = scratch, and make sure that you don't snap the plastic edges (if the knobs are plastic, that is).