Depends on where you are starting from. If you are going to replace the top coating, it doesn't hurt - but a little goes a long way. If you use sandpaper that is too course, you'll spend more time on levelling the scratches. Buy wet&dries in various grit sizes: I tend not to go lower than 400 (maybe 280) for coatings, and work up in between coats to 600, 800, 1200 and 2000 for polishing. I always sand wet and let the wood dry well before applying anything. Feel free to P.M. me a couple of pictures, as it's hard to figure out where you should start from text alone.
Edit: Forgot to say that if the above sounds like a lot of work, that's because it IS time consuming. Skimping on prep and painstaking detail will show in the end result. As I have more on my mind than time on my hands I tend to do this stuff on winter evenings before the fireplace - sort of a mindless "wax on, wax off" zen thing