Standard passive tone controls are variable treble attenuators; they work by removing treble. They siphon from the hot signal only those frequencies that make it though a certain strainer. They send those frequencies to ground (where they are inaudible). In other words, they are just controlled "leaks" from the main signal to ground. The potentiometer is the siphon valve...and the capacitor is the strainer.
The capacitor value is what determines the coarseness of the strainer. The lower the value, the finer the strainer – the higher a frequency must be in order to pass through the capacitor and leak off to ground.
Therefore the capacitor value you use is really just a matter of taste. Use a higher value (e.g. .047 uF) if you want a very bassy, muffled tone when you turn down the control. Use a lower value (say .022 uF) if you want a slightly less treble-attenuated tone. Go even lower to get a tone that mainly just rolls off the top end, kind of like a snarly cocked wah tone.
In a guitar circuit, capacitor material does not affect tone – only the actual value/s of the capacitor/s used. Therefore it pays to spend the money for tight tolerance caps (e.g. 5 percent as opposed to 20 percent), but not to pay for caps made of a certain material. Also, go for the lowest voltage you can find, as they will usually be cheaper. The Orange Drops most guitar parts suppliers sell are 600V or 400V, which is ridiculous. All ratings that high do is to make them larger and more expensive.
FWIW, my go-to cap value is .01 uF. I usually find the higher values too muffled, though I will sometimes go with a lower value, like .0047 uF (4700 pF). My go-to caps are 100V, 5 percent tolerance Orange Drops. Overkill, yes, but for under a buck a piece for a cap that I don't have to bother measuring, they're a good option IMO.
