Sand in small areas, use a squeegee often, and listen for an eerie squeak, that's broken grit building up. Making really deep scratches.
Use a steady stream of water, from a big sponge while sanding or a small stream from a hose. Use your fingers sideways, or buy sanding pads made by a company named: Motorguard. they're hard on one side, and soft on the other.
At all costs, keep the sandpaper clean, because the broken off grit will make the scratches so deep, you'll never get them out!
Squeegee often, to see if it's smooth enough to move on to the next area. When done, use MaGuiars #2 and buff lightly with a terrycloth rag, available at AutoZone or advanced auto parts, until you see a good gloss. Then use MaGuiars #9 to remove any haze and swirl marks, you'll be able to see your self and shave.
Refinish King
PS Any coarser paper will require the use of an electric buffer.