Depends on what sort of print and what it is you want to clean off.
In general:
Most things will come off RC if you breath on it and gently polish with a soft cotton cloth.
It works quite well on fibre base as well.
For more stubborn marks like fingerprints on RC use isopropyl wipes and polish off any residue with a soft cotton cloth.
I've had good results using isopropyl wipes on fibre base to get rid of mould marks.
If there is a lot of dust or grit on the prints you should get rid of it first using compressed air and a brush. Any particles still stuck on try carefully scraping them off with your finger nail.