Potentiometers:
Before I get into controlling tone and volume it is better to know about potentiometers first, as they are not only the knobs you turn to control tone and volume with, but they come in different flavors.
A potentiometer is a variable resistor, the name comes from metering electrical potential (voltage). You are most likely going to find them at 250k ohm with single coil pickups, or 500k ohm for humbuckers, but that is not a must, it is just industry standard, and in reality you can have in between values, and go as high as 1M ohm, depending on what results we are aiming for. There are also ways to make one potentiometer work at different values depending on the switch position in relationship to how many coils are on, and blend potentiometers that control two pickups or coil arrangements at the same time, turning one up and one down with both on full in the center position.
There are different ratios at which potentiometers can be made to work at. There are the linear type, where the value changes in unison with the turning knob, at half a turn it is at half value, but some people don't like that. Then there is the audio taper kind that use a logarithmic slope, where the resistance increases more at first, and less and less as the knob is turned, so if turned half way you are already at around two thirds of its value. since they are designed for home audio and not guitars, some people don't like them either including me. Dimarzio came up with a solution called custom tapered potentiometers specifically for guitars, with a slope more agreeable for most people. Those are only made in 250 & 500K ohm versions. You can have which ever flavor you like, and even different ones for tone and volume, as it is a matter of personal preference, and personally I like linear pots throughout, but we can play around with that to find your preference. there are lots of options to put control in your controls!
Tone control:
Controlling tone is a strange thing as it can be done to a great extent, but is often not used much by most players. Maybe because almost all tone controls these days are "low pass" filters that drain treble via a potentiometer to ground through a capacitor. Crack open an instrument built before 1965 and you are more likely to find much more components in there used to shape the tone, and if you listen to music from around that time, you can hear it being used more often too. Sure, there is a lot of tone control going on via effects pedals and rack mount units these days, but there is a difference in the end result, depending on where it is done, just like it makes a difference in which order your effects pedals are plugged in.
As I stated, almost all tone controls in guitars are "low pass" filters, and as the name states the low's pass through unaltered, and the highs are filtered out, so what ever happened to "High Pass" filters? Well they still exist, and are a mere rearrangement of the same potentiometer and capacitor, so it is possible to have a tone control filter out mid range or bass instead of treble. By using one of those fancy dual potentiometers, you can move from low pass to high pass with just one knob! How about a rotary switch that changes multiple filters of your tone circuit, like BB King has on his Gibson ES335 (Lucille)? That is called a cadence switch, and it can be done with toggle or blade switches too, with three or more settings.
Basically, using components of different values, changes what frequency's are filtered out, and by how much, as the resistance of the potentiometer changes, but since the pickups are coils, and their values vary too, based on their construction, the results of the same components of a tone control circuit will have different results on different pickups. So there is no sure result on what will happen with a 250K ohm potentiometer, with a 0.03µF capacitor, and that is where trial and error comes in.
The most effective and versatile tone control can be achieved with preamp's, as they are not merely meant to amplify the whole guitar and overdrive your amplifier, but rather boost certain frequency's rather than cutting others, which makes a big difference. Although more likely found on basses, as they tend to have flatter frequency ranges, guitars can benefit from them too. Keep that in mind if you realize that you don't want less trebles, but rather more bass.
Volume control:
Controlling volume of the instrument is standard, but do you want to control each pickup individually, or just the whole output of the instrument? The latter is easiest to work with, but you may want different, and given the many types of potentiometers, there are many options.
Control group switching:
Ever see a Fender Jaguar from the sixties? They can be switched between groups of controls, there is a volume and tone control for the rhythm pickup, and a separate set for the lead pickup which has an additional bank of three switches with two more tone stages and one switch to add in the neck pickup. That way you can preset the controls for a song and switch between the two control sets, and change them for the next song and the switch goes between two completely different settings. It is also an option you may want to consider, that has great uses for the recording studio, so you can switch between presets without having to mess with knobs and switches, possibly throwing you off from playing. With physically small potentiometers and switches it can be taken quite far, and give you more than two main settings.