If you are not a woodworker I wouldn't try to do this yourself! Ideally you need a router and template for the pickup cavity and a really long (2 ft/55 cm) drill to connect to the control cavity. The reason you need a drill this long is to be able to drill at a shallow angle. If you have a guitar with a scratchplate it is a lot easier, as the scratchplate will hide the wiring channel (in this case you cut the channel with the router too).
If you are a very skilled cabinet maker, you can cut the cavity with a chisel, but you reall have to have a lot of skill to do this without messing up the finish or the wood in the body.
Depending on the value of the guitar, the cheapest option might be a luthier!