Remove the original finish with sandpaper. If it has a thick finish, you must use a thick-grit sandpaper, somewhere between 60 and 100 grit. If the finish is thin, a 200-grit sandpaper may be enough to remove it. The table top will have a dull appearance once the finish is removed.
Smooth the entire surface of the table with 200-grit sandpaper. An electric belt sander can speed up the process for this, but it isn't necessary.
Brush the dust off the surface of the table with a broom. Wipe the surface with a moist washcloth to pick up any residual dust.
Brush on a coat of wood varnish with a paintbrush or paint roller. Brush in one row at a time to ensure the varnish is even on the entire surface. Let the varnish dry for the recommended amount of time for your particular varnish, usually between four and eight hours.
Apply a second coat of varnish after the first coat dries. Let the second coat dry for the recommended amount of time. Continue to apply varnish one coat at a time until you are pleased with the appearance.