You can waste a lot of plywood if you don't make a cut diagram or cutting plan before slicing into a piece of plywood. One of the most common errors is not thinking about which way the grain of the surface wood is going. In some projects, especially with veneer finished plywoods, this is critical.
I have found that learning how to play with paper dolls is the best way to go. I actually cut out pieces of paper to scale for every piece I want to cut. Then I place them on a scaled piece of plywood. This allows me to juggle a lot before I ever cut a single piece of wood. It is sometimes surprising to discover which combination of big pieces and little pieces makes for the most efficient use of wood, all while respecting grain direction.
Once you get your pattern so it looks like it will all fit, then do the math. Carefully add up all the sizes of finished cut wood and don't forget to add in the kerf thickness of your saw blade, to see if it will in fact fit into 48 or 96 inches. You will often find that you are 1/8th of an inch out and have to start over, or at least move a piece.