Use only water or oil on a soft rag on the machine. Many things can destroy the decals and the finish. Be sure that anything you want to try is safe before using it.
Sewing machine oil is often all you need. I wouldn't use really old oil; what you use on your other machines would be fine. It does need to be sewing machine oil; this oil is much finer than other types of oil.
Only certain featherweights require lubricant (comes in a small tube made by Singer). Again, learn about this before using it.