I recommend keeping around a can of DeOxIt D-series:
DeoxIT® D-Series contact cleaner dissolves oxides and sulfides that form on metal surfaces. This restores the contact’s integrity and leaves a thin microscopic layer that protects the metal. Special additives improve conductivity and prevent dissolved oxides from re-attaching, keeping them in...
caig.com
This stuff is the equivalent for old electronics that having a can of WD-40 is for sorting out aging/rusty mechanical gizmos. I most recently used it to fix a flaky scroll wheel on a digital camera! Another example would be a flashlight, where oxidation has built up on the contacts with the batteries.
Be sure to follow the directions, including safety precautions.
Use with lint-free cloths. In a pinch, Q-tips can work, but require more care that they don't snag on anything and pull apart.
P.S. It's usually not worth going the extra step to use DeOxIt Gold. If you read the directions carefully, they say to apply it
after regular DeOxIt D-series. If I needed to clean off the contacts of a CPU or DIMM, where someone left a big, greasy fingerprint, I'd go to the trouble of using Gold. Otherwise, no.