1. Cut the drywall sheet to size.
2. Using a dark color lipstick, outline the four corners of the box with a thick layer of lipstick. If you're cutting out a circular opening (as shown below) outline the entire circle.
3. Push the drywall into place firmly enough to leave an outline on the back.
4. Cut outside the lines with a drywall saw. Smooth with a rasp if necessary.
5. Secure the drywall using screws. Make sure to put at least one on the stud adjacent to the box.
Next, see these sections:
Hanging drywall - Drywall installation tips.
How to hang drywall - A step-by-step guide to hanging drywall.
How to cut drywall - For the basic, straight cuts.