If you're using any type of power saw (rotary, table, etc.) use as fine a toothed blade as you can find. The more teeth per inch the better. Then, before marking the cutting line, run a length of masking tape (the kind used by painters) down the length and place you're cutting line on top of the tape. The tape will help keep the plywood from splintering. Additionally, if you're cutting a longer length be sure to support the board with enough saw horses to keep it from sagging in the middle... Works for me...