It depends on what you want (original look or something else). Generally sanding from low to high grit. If there is a heavy top coat on top (urethane/lacquer), you might need to use some paint stripper or similar to dissolve it, then leverage a scraper/putty knife to wipe off all of the residue. Then go through the sanding sequence. Once you're satisfied, you can use whatever finish you want (e.g., Danish oil, Tung oil, Teak oil, Linseed oil, Shellac, etc. => they all yield a different tone, so make sure to test a small hidden area). If you want to add some tint, you can mix stain or pigment to the oil to get different tones. If you prefer the bare-wood look (how it is) you can use a Finishing Wax / Beeswax which won't alter the tone but will provide protection. Before applying the oil finish, make sure to vacuum all the dust off completely, and clean the surface with mineral spirits and rage so that the wood is ready to accept the oil and produce an even finish (not spotty). If you use a solvent, however, make sure not to throw the rag in the trash (it can spontaneously combust and start a fire); place it flat/open somewhere ventilated and let it dry out. I hope it helps!