http://www.nikonchat.com/nikon-camera-body-cleaning/

What is the best way to clean the inside of a DSLR camera body?
I have a nikon d3000. I was interchanging lenses today and noticed a bit of dust on the mirror inside the camera body. I always put the cap on after I interchange a lens. What is the best way to remove this dust?
Thanks in advance,
-G.B.
Unless its really bothering you I suggest just ignoring it. If you absolutely positively find its just too annoying to ignore then hold the camera with the lens mount facing down and use a small bulb blower to dislodge the dust. DO NOT touch the mirror because its a front-surface mirror and rather delicate.
When changing lenses keep the camera pointed down and avoid windy, dusty conditions.
Nikon D90 Digital SLR Camera Body + nikon 18-200mm vr II Lens + 16GB Card +