Make cuts across the contours of aluminum siding with a radial arm saw or a chop saw fitted with a panel blade. The panel blade has a very fine tooth that allows smoother cuts in the aluminum siding without tearing and snagging.
Install the panel blade backward in either power saw if you are still experiencing snags. This is a common builder’s trick and it works because the teeth on the blade are cutting from the smooth side instead of the jagged side.
Use straight tin snips for cuts along the width of the aluminum siding. Underneath windows, doors and eaves, you will likely need to cut the siding horizontally in order to fit it into the smaller space. Cut the top edge of the siding so the bottom feature strip will appear uniform and match the other rows.
Cut with red-handled tin snips when you are using your right hand and you want the portion of the aluminum to the left of the tin snip to rise. Do just the opposite with the green tin snips when you want the right side of the aluminum to rise. It takes some getting used to when alternating hands to cut but once you get the hang of it the work will go quickly.
Try using a niggler for cutting long straight sections horizontally. A niggler is a hand tool that vibrates two small blades up and down at high speed and allows you to cut a straight line in flat stock siding. Nigglers will not cut through the contours of the siding, however. For those cuts, use tin snips or the power saws.
Follow the general rule of using the big saws only for cuts that extend all the way from the top to the bottom of the siding. Since both the radial arm saw and the chop saw are difficult to control with precision when ending a cut, use the tin snips if you are trimming the siding to fit around windows, or vents.