There are many places that have various diagrams/mods etc. and I'll admit they're not easy to find.
Try http://guitarelectronics.zoovy.com/category/wiringresources/ for some good basics, as well as the free info on StewMac.
If you've got a P/J and want to add a hum and wire all three to individual switches- that's not too bad. Don't have a diagram right off, but here is a quick explanation:
Each of the 3 switches need to have the + connected to a common wire that goes to the volume pot. You have a 3 toggle already so it will be pretty easy to find the common wire since it's the one going from that switch to the vol pot. Assuming you're going to replace the 3-way with on of the new switches - bring the existing common to the + on the closest switch, you'll then solder a jumper wire from that + to each + on the consecutive switches (see, this one's easy). Connect ground wires to the other side of the switch and all should be complete.
This gets a little more complex when you want to throw caps and stuff into the mix.
If this were a 4-wire HB with coil splitting, then you could use the existing 3-way switch in the mix so that not only would you have on/off, but on/off/split.