Cutting a clean, round hole in plywood is not as simple as it sounds. If you try to freehand cut a hole in plywood with a jigsaw, you ultimately tear the plywood and the results are anything but round. You have to use a tool made especially for cutting holes: a hole saw. A hole saw cuts perfect holes every time. Hole saws come in sizes ranging from 9 cm (3/8 inch) to about 60 cm (24 inches).
Locate the exact centre where your hole will be located and mark it with a pencil.
Place the hole saw into the drill and tighten it with the drill chuck.
Place the tip of the pilot bit of the hole saw directly on the mark. Pull the trigger and allow the pilot bit to establish the cut as it penetrates the wood to a depth of about 6 mm (1/4 inch). When the cutting edges of the hole saw begin to cut, ease up slightly.
Push on the back of the drill as you hold it tight. Lean into it with your shoulder to stabilise the drill. Hang on to the front of the drill with your other hand for additional bracing.
Rock the drill gently from side to side. Check your 90-degree drill-to-plywood alignment by glancing at it sideways as you drill. When the hole saw is within about 3 mm (1/8 inch) of penetrating the wood, slow down and let the hole saw gently cut away the few remaining fibres to prevent tear-out on the back.
When a hole saw exceeds about 7.5 cm (3 inches) in diameter, they are referred to as "circle cutters." If possible, place another piece of plywood behind the hole being cut or underneath it to brace the hole saw as it exits the wood. Clamp it there or hold it there with your other hand if you can. This is to prevent tear-out on the back of the plywood.
Always be aware of possible kick or binding of the drill. 1.2 cm (1/2 inch) drills have more power than ordinary hand drills and can twist your arm if they bind. Make sure you have an adequate grip on the drill at all times. Wear safety glasses.