Equip the saw with a diamond blade. These blades will easily cut through a ceramic dinner plate.
Pour water into the trough of the wet saw. Refer to the instructions for your particular brand of tile saw to determine how much water you need.
Mark the dinner plate where you would like to cut it with a grease pencil. This mark will be easy to remove later, but it will not wash off easily as chalk would.
Place the dinner plate onto the wet saw directly in front of the blade. Line the blade mark on the plate up with the blade before you begin cutting.
Turn on the saw so that the blade begins to spin.
Push the dinner plate into the spinning blade along the mark you made. Gently guide the plate but avoid forcing it into the blade.