Well, to begin talking about this topic, let me say that there is no right or wrong. It's a matter of experimentation and using your ears as a compass. The most common values used in electric guitars are 250k and 500k.
My rule of thumb for this matter is very simple. The higher the value of pot, the more treble sound you'll hear. For example, you could say 500k pots are best for humbuckers on Les Pauls and 250k pots are better for single-coils on Strats. This is because, in the first case, they add brightness to the big low-end of the Les Paul. In the second case, they tame the shrill highs in a Stratocaster.
But does that mean you can't buy 500k pots for Strat? Well, of course, you can, maybe you even find a signature sound. Believe me, besides the soldering time, it's a very cheap tone experiment to do.
Using the correct pot value is pleasing to the ear – we don't want muddy sounding humbuckers, or piercing single-coil pickups. So, our pots help compensate and shape the tone right from the get-go.
There are alos other values such as 300k and 1meg, but we won't talk in this one.
