Hi. The first thing to do is to wash the top with household bleach mixed about 10 to 1 with water (add 1 cup of bleach to 10 cups of water)and rinse well. This should get rid of the stains. Next is to sand with a belt sander starting about 80 grit, then 100-120 grit, then 150 grit. Use a vacuum ordamp sponge to get rid of the sanding dust when changing grits. If your top is hard maple, this will be difficult to sand as end grain maple, in particular, burnishes rather than sands with the finer grits. Sand just enough to remove the cuts and run a damp sponge over the area every so often as this will show up the remaining cuts and scratches. Finally, apply a couple of coats of mineral oil and wiper them off after about 5 minutes with a clean rag. This will leave a nice shine/glow on the surface. You can repeat the mineral oil every couple of months, if you wish.