Dust accumulates on electrical components and will cause premature failure to excessive heat build-up.
Use a small hand vac and carefully pick up the dust from the components from inside the case, You can waste money on a can of compressed air, but take the thing outside first.
Also be sure to keep the vents clean and unobstructed. Some vents will have filters build into them: remove the filters periodically and clean them. Don't shove the case so far into a corner or cubbyhole that air can't circulate through it.
Look on TigerDirect.com or NewEgg.com for specialized vacuum cleaners that are intended for cleaning electrical equipment. A small hand-held house vac with a tiny nozzle should also work just fine. We don't need surgical cleanliness.