Draw the lines onto the drywall where you need to cut with a pencil. Use a straight edge when making your lines so the lines are straight.
Place the blade of the ax side of the drywall hammer over the cut line. When starting a hole, ensure the top of the blade is at a corner.
Rock the ax blade end to end with the handle, while holding pressure with one hand on the hammer head. The pressure and rocking action pushes the blade through the drywall.
Smack the hammer end of the drywall hammer with a rubber mallet a couple of times, instead of rocking the blade. Lift the drywall hammer out of the drywall, and move it down the cut line.
Continue striking the drywall hammer with the rubber mallet, and moving it along the line until the hole is cut complete.