I'm building a table and finishing it with a high-gloss polyurethane. I've seen how to apply the poly and what to do between coats, but what do you do after that last coat? Is it done? Do you wet sand it with 2000 grit? Do you wax it? What will give the best results for smoothness and shine?
In most cases, if you have done all the right things like sanding and cleaning between coats, you should be done and have an excellent smooth glossy finish. Any further sanding or polishing with any kind of abrasive will dull the finish. Normally urethane does not need a wax. After some use and a good week or two of total cure time, a regular furniture wax like Pledge or Butcher's Wax will help keep the finish clean and shiny. Never use an abrasive polish. If the finish dulls over time, buff it with 220 grit paper and give it a fresh coat of urethane. This should not be required for a long time depending on usage.