Short of steaming dents and patching the wood, it's not that hard.
Never use sand paper...you'll change contours and eliminate or ruin stock stampings or cartouches.
Mineral spirits rubbed onto the wood with 000 or 0000 grade steel wool, will removed all the grease and years of grime to reveal a much prettier wood. Go easy around the stampings.
If the wood was varnished or polyurethaned, use an appropriate remover for that but don't over do it. The final bits can be taken off with the spirits and wool.. Shellaced wood succumbs to the mineral spirits and wool treatment pretty well.
After getting the wood as clean as you can, rub a coat of Boiled Linseed Oil or tung oil on with a rag. Rubbing it, not just wiping it on is the secret. I use full strength BLO, some use 1/2 BLO 1/2 thinner. You'll probably find that the first few applications get sucked into the wood very quickly. BE sure and coat the inner parts as well to make sure that the wood with withstand moisture evenly, inside and out.
If it soaks right in, keep giving it more coats until it appear not to soak in and takes a while to dry. Then sit it somewhere over night.
Next day, rub it with 0000 wool and give it another coat. Set it aside for 24 hours. and repeat until it's as smooth and shiny as you want it. It may take 8-10 coats.
It's easy to get a nice finish, you just can't rush it.