Here is a good place to show how to block a guitar when working on it face down:
Cut 2"x2" blocks about 12" long. Wrap them in wax paper and tape it on with masking tape.
Set the guitar up on it's side to determine how the blocks should be laid to elevate top parts off of the work bench. If the top of the guitar is arched then rolled up bath cloths or towels can be added to the ends of the blocks for support. If the work on a guitar of any type is going to be forceful, then it's a good idea to use rolled up wash clothes, towels, T-shirts, etc. to protect the guitar.