I use this jig, which I made from leftover materials, to cut plywood into manageable sizes. Melamine provides a slick surface for the saw to ride on and shelf standards guide the saw base in a straight line.
The stops at the end of the guide keep me from sawing too far. Two boards (A) help square the guide on the sheet of plywood, but I still double-check the guide’s position by sighting through the 1-in. holes to make sure the saw blade lines up with my pencil line. Two more boards (B) hook over the top of the plywood and provide a simple way to secure the guide to the sheet of plywood.