Remove everyday dirt and dust from the wood with Prelude Orange Oil or a similar product. Use Prelude Furniture Cleaner and 0000 steel wool for heavier cleaning, working it lightly over stubborn areas of old wax and polish to avoid scratching. As Brian Hingley points out, 0000 steel wool can be used to produce a satin effect.
Fill dents with Liberon Wood Filler, or a similar product. Alternatively, use a mixture of sawdust and wood glue. Allow to dry then stain, varnish, wax or paint as required to match the existing finish.
Cover scratches with Ronseal Colron Scratch Remover or similar. Follow Jeff Bredenberg's advice and use a stain pen (also called a scratch remover pen), alternatively. Hide the scratches by coloring them in with a wax crayon of the same color as the cabinet, for a cheaper version of a stain pen.
Revive wood, especially antique wood, with Rustins Finish Reviver or something similar. Alternatively, use a mixture of 1 part malt vinegar, 1 part methylated spirit and 1 part linseed oil.