Work you way up to 220-240 grit sandpaper sanding with the grain until wood is as flat as you can get. No need to go finer as you get the shine in the finish not the wood. Fill with wood filler and sand with the grain. If there are some low points use an artists paint brush and fill the lower points and I then use a fine Scotch-Brite wrapped around a block and sand slightly across the grain. The Scotch-brite wont hurt your previous sanded finish and repeat until the whole surface is dead flat. Then apply a sanding sealer so you get an even stain. Apply 2 coats of poly with a brush and sand with 600 wet and dry. If there are any low points then repeat but if the surface was finished properly with filler and sanding then just apply 2 coats with foam brush after using a normal brush giving you a total of 4 coats. Sand with 1500 grit wet and dry and apply a final coat with a foam brush. Sand with 1500 wet and dry to make sure it is dead flat and leave until completely dry, maybe a month depending on weather and brand of finish. Then polish with cut and polish compound and it should be like a sheet of glass. Well that's how all of mine are done.