I have made dozens of sheets of ground glass up to 8x10.
The easiest method is to make two at a time. Obtain some 600 grit, or finer if you can find it. It is available at hobby shops which cater to rock tumblers. Put about 1/2 teaspoon on one sheet of glass. Add about an equal amount of water.
Place the second sheet of glass on top of the first, and with smooth rotary motion, and only moderate pressure, start grinding. if wheyou check one area has not been ground equally, use a little more pressure in that are as you continue to grind.
Not difficult, but be patient.