There are so many different finishes on guitars that you almost have to be a chemist to
understand them all so I'll try to be general.
It's best to use a clean lint-free cotton cloth and wipe your guitar off when done playing. If there is an area which will not come clean, moisten the cloth a little. Never use paper towels.
Polish should be used if the above doesn't work. I use Martin Guitar Polish. If you have an older guitar with a varnish finish, try to find a polish with lemon oil in it. If your guitar has cracks in the finish you may want to get professional advice. The polish could get in the cracks and make a mess of the wood.
If your fingerboard is not finished, (most aren't), apply a small amount of lemon oil on a
rag and rub it in to prevent cracking.
Also read my Tip 80 for satin or flat finished guitars.
Gman ( o )==#