Step 1: Sand the top and back with 220 grit sandpaper.

Use a random orbit sander, or do this by hand using a sanding block. Do not use your fingers on the sand paper because the paper conforms to your fingers and leaves an uneven sanding job.

Step 2: Sand the top and back with 320 grit sandpaper, following the same principle outlined above.

Watch for scratches in the wood surface. You want to remove all obvious scratches. The amount of time you spend on the preparation phase will pay off in dividends later when you're finishing with oil, lacquer, or whatever you choose.