A jigsaw will allow you to saw complex curves, cut circles and other shapes in panelling and even saw thin metal sheets. With the right blade and proper guidance, the jigsaw or sabre saw cuts smoothly and on the mark. Use the electric jigsaw freehand and without the right support, and broken blades or splintered work are common.
Wear eye protection and keep your fingers away from the blade, both above and below the workpiece. Use sharp blades appropriate to the work--don't use large toothed wood sawing blades on metal or fine-toothed metal sawing blades on wood. Take battery packs out of portable machines or unplug corded models before changing blades or adjusting the base angle.
Know where your power cord is before you begin. Snagging a power cord between a sawhorse and a piece of panelling could put it in the line of the cut. Expect hazards when you cut into a wall or any panel already in place. Wires, nails or plumbing could be in the way. Hold the machine by the non-metal parts to avoid accidental electric shock. Drill a pilot hole big enough to insert the blade, and use a pen light to check for obvious dangers.
Whether cutting panelling or solid lumber, support the work near the line of the cut. Place the base plate of the saw firmly against the work before you hit the power switch, but don't put the saw blade in contact with the wood until the blade is in motion. The saw's teeth cut on the up stroke and should pull the saw down against the workpiece. If you force the saw into the work, the saw will lift on the down stroke. Results will be rough work, vibration and possibly a broken blade.
For straight cuts, clamp a straight-edged board on the good side of the line, and use that to guide the base of the saw. The board will act as a fence and stop the jigsaw from wandering into the workpiece. For scrolling cuts--sawing complex shapes and curves--freehand control is often the only approach. Clear the space around the work to avoid trips and awkward positions during the cut. Clamp the workpiece down and support it well. Don't try cutting a curve too tight for the blade--it will only overheat and bind.
Near the end of a cut as the workpiece separates from the waste, the wood may shift and bind on the blade. If there's a problem, back the jigsaw off a little and turn off the power. Don't pull the saw out of the cut until the blade stops moving. Reposition yourself, support the work properly and then place the blade back in the kerf. With the saw in place, turn the jigsaw on again, and finish the cut.