This will vary greatly depending on what sort of printer you are trying to clean. Most printers will come with instructions specific to them and these must be taken into account for various reasons. Specifically, the design of the printers will cause great variance in the type and style of cleaning that is appropriate with the various portions of the printer.
Generally rules that will apply to most (but not all) printers are these:
1) Don't use compressed (canned) air!
Especially with laser printers, but still valid with most other types, compressed air will blow paper dust, spare toner, and any other foreign objects into the print heads, motors, fuser wires, and many other components that do not work well when buried under fine layers of dust. I learned this one the hard way. Dot Matrix are probably the least susceptible to the problems associated with blown dust simply by nature of their much greater mechanical tolerances and lower expected output quality compared with other printers.
2) Wet/Moist cleaning wipes are OK on the outside only!
Moisture is only slightly less problematic than dust, mostly because it'll probably evaporate. However, moistened wipes will usually smear and leave residue which is not good for electronic's life expectancy. On the outside they're just fine though. And in an office environment it can be good for office hygiene to wipe the shared printers down every once in a while.
3) Do not use solvents on the rollers!
Any sort of solvent or cleaner will generally dry out the paper rollers, decreasing their lifespan, degrading paper handling, increasing jams and other equipment failure. The only liquid that should ever be used on paper rollers is none. Even rubber conditioners will cause the rollers to become more sticky than they should be, causing problems. If the rollers are having trouble, wipe them with a dry rag to remove any built-up paper dust, or order a replacement kit (usually availble for laser printers).
4) Dry wipes are your best friend.
Lint-free towels (old socks are great for this, especially polyester/cotten blends with a fine enough weave) are the best tool for cleaning anything out of printers, for wiping the rollers, and any other use inside the printer.