Is the finish in fair condition and would like to keep the stain color(if stained)? If so you can lightly sand with a 220 grit paper, tack off dust and refinish. If you try to sand out any scratches etc. in the clear coat be sure not to get into the stained wood, if you feel you are, go on. If you use a polyurethane check the label of the brand you will use to be sure it is compatable with other finishes, unless you know it is an existing polyurethane finish.