There are many ways to shield and ground a guitar. I could write a book, (hummmmmm) Or did I..
I'll get into more details in the future. For now here is a nice photo of a copper shielded guitar and pickguard. Notice the seams are soldiered and it is burnished down in the cavity very clean and tight. There is a wire connecting the copper to the jack ground.
The most important thing about any shielding job is to ground what ever material you use as a shield otherwise it will act as an antenna and the noise you are trying to keep out.
I can't tell you how many times I have seen aluminum foil stuffed into the cavity of a guitar. If the guitar is luckily enough to even work it is very noisy. Another odd thing I see more often than that you would think is manufactures using shielding paint in pickup and tremolo cavities, sometimes even for cosmetic reasons with no ground attached. The pickups are a set of J. M. Rolph very authentic vintage Stratocaster pickups. We are also installing his proprietary noise reduction system (not in the photo)