Cut the Drywall
After measuring carefully, score the surface with a utility knife and sharp blade, making sure to cut through the top layer of paper (Image 1). Once the board is scored, simply bend and snap it. That will leave it hanging by the bottom layer of paper. Use a sharp blade to make a clean cut through the paper layer (Image 2). For more complicated cuts, like holes for switches or vents, use a saber saw. After measuring and marking the board, carefully sink the blade directly into the board (Image 3). If you don't have a saber saw, you could also use a small, sharp-pointed hand saw.