I use isopropyl alcohol to clean my keyboards (I don't have any pad-printed keycaps). I dip q-tips into the alcohol and carefully clean the surface of each key while they are on the keyboard.
If I need to clean a new keyboard find, I apply the same method but remove the keycaps and wash them in water first to remove surface grime, then wipe off the entire cap with alcohol. If ever I found a pad printed keyboard I like (or am asked to clean for a friend), I would do the same method but replace the alcohol with water.