Well, there is no right or wrong answer to be honest. It's a matter of experimentation and using your ears. But there are guidelines...
The most common pot values used in electric guitars are 250k and 500k.
The higher the value of a pot, the more treble frequencies will be heard. The basic best advice is that 500k pots are best for guitars with humbuckers, such as Les Pauls, and 250k pots are better for guitars with single-coils, such as Strats.
This is because the 500k pot will add brightness to the big low-end sound of a Les Paul. Whereas the 250k pot will tame the shrill highs of a Stratocaster.
But does that mean you can't install 500k pots on Strat?
Well, no, of course. You might even find yourself a signature sound. But it will probably be too piercing for most guitarists' tastes.
Using the correct pot value will make your guitar tone pleasing to the ear – no one wants to listen to muddy-sounding humbuckers, or super-toppy single-coil pickups.
