Mineral oil works great. When I'm done shaving, I put a drop of oil on a tissue and "strop" against it-- my goal is to oil the blade's edge to protect it from corrosion. Then I wipe down the rest of the blade since I happen to be holding a tissue with oil on it... I doubt I need to do that as I don't live in a very humid place... but it does not hurt.

I just wipe it dry with a clean tissue before I strop with it on my next shave.

-Chief