IPA based cleaner is good for removing gunk: Flux residue, potentiometer crud, spilt tea, that sort of thing. Proper corrosion (eg. from loose contacts arcing or from leaky batteries) needs a bit more elbow grease, for which Torslanda has the right idea.
I have an ancient tool (from the days when Tandy were the old Maplin) with a tiny wire brush on one end and a sharp scrapey-thing on the other, which is handy for this sort of job.