1.  Is the dust on the lens or did it get into the camera?
2.  If it's just on the lens start by using a blower and see how much dust
and dirt you can remove.
3.  If that won't do it you can try a soft lens brush.
4.  If that still won't do it use some lens tissue and lens cleaner,
available at any photo store.
5.  If the dust is in the viewfinder (focusing screen), you should be able
to blow and brush that out.
6.  If it's on the mirror you can clean that, too, but be very careful.
It's a surface coated mirror and is easily scratched.
7.  If you've cleaned everything else, and you still see spots, you've got
dust on the sensor.  Try using a blower first.  A hand blower, and not
canned air.  That will often do it. (Look in your manual as to how to expose
the sensor for cleaning).
8.  If not, you have three choices.  You can try one of those brushes made
for cleaning the image sensor.  You can use one of those kits for cleaning
the image sensor.  You can send it to the factory.

Cleaning lenses should be something you learn to do yourself.  Lenses get
dirty all the time.  Buy some lens tissue and cleaner and the person in the
photo store who sells it to you should be able to show you how to clean a
lens.  Just don't spit on it and use your shirt. :-)

If you have to go inside the camera you must have the confidence to go for
it, or just take it in.  Gone are the days when you could just open the
camera, set the shutter to bulb, and blow the hell out of it with a can of
air.  It is a gamble to go in there and do anything beyond what the owner's
manual tells you.

Ben,
Actually a plastic bag is not a bad place for the lens to be, generally
clean, and plastic generally has an electronic charge that catches
dust. Anyway, graininess when you look through the view finder comes
from a lack of light at the ground glass, the lens would have to be
filthy to cause this. Did your camera get set to stop down the lens,
this would cause this or have you been using a large aperture lens on
the camera and then switch to the slow kit lens? Again it would really
be a discusting film on the lens to cause the syptoms you describe.
Clean the lens with a blower or use isopropyl alcohol on a cotton ball,
make certain it is cotton, an gently wipe off with a dry cotton ball.

good luck
Tom