Support the plywood on both sides of the cut with sufficient sawhorses or other holders. When an unsupported side of the board wobbles up and down the wood along the kerf -- or track of the saw -- it will chip and splinter.
Cut with the good side of the board facing downward.
Don't force the blade into the wood. Let the saw do it's job of cutting.
Mask the bottom side of the board along the planned cut with an easily removed, 1-inch-wide masking tape. Remove the tape as soon as the cutting is finished.
Sandwich the veneered side against another sheet of plywood and clamp them together before making the cut. Face the two pieces of wood so that the veneer is facing downward.