#1
Does this mean to just put some aluminum foil in the cavity? Or do you need to connect the foil to some part of the electronics?
Guitars:
- Ibanez GRX40
- Ibanez RG1570 MRR
- Eddy (Plywood Stratocaster Copy)
- Dean V Metalman
Amps:
- Marshall MG15 DFX with custom speaker
- Vox AD30VT
Gear:
- Boss DS-1 (Keeley modded)
- Vox V848 Wah
- Digitech RP80
#3
One of the best write ups I've found is here

http://www.guitarnuts.com/wiring/shielding/shield3.php

any and all shielding you use must be grounded to the electronics, otherwise it's useless and may contribute to hum. I shield the pickup cavity and line the back of the pickguard, using heavy duty aluminum foil and spray glue. Be extra careful to mask off any areas you do not want glues, the spray stuff gets everywhere. I used it only on the aluminum foil, that lets me peel it off later if necessary and still sticks well.

To do a really proper shielding/hum reducing job you would need to rewire the pickups and shield the body, and go with a star ground scheme, to eliminate ground loops. Just shielding the pickguard and cavity while making no wiring modifications made a world of difference on my guitars. Instructions for wiring with star ground are all over the net, including the above link, google it if you want more.