If you have a digital SLR, sooner or later and whether or not you change lenses a lot you are going to end up with dust spots on the clear pass filter.
Here's some good advice

http://www.cleaningdigitalcameras.com/

From my own experience, there are always going to be a few spots of muck on the clear pass filter, often wrongly referred to as the sensor, but actually a bit of glass in front of it. For the most part these spots only show up in light areas of the picture (typically the sky) and are easily dealt with in Photoshop with either the clone stamp tool or spot healing brush so there's really no need to clean the clear pass filter a lot.
Some situations will show up dirt more obviouly eg using a wideangle lens on a small aperture or in subjects where there is a lot of sky. One situation I would always clean the CPF is before an airshow, to avoid tedious retouching in Photoshop afterwards.

So....how to do it?
First, the check to see if there is dirt.

Go take a picture of a blank sky at F22. Dowload the picture, blow it up 100% and you'll soon see any dirt. Save the picture....you'll need to refer to it later.
Next make sure the camera's battery is fully charged. This is important because if the battery exhausts during the cleaning process the shutter and mirror can close onto the cleaning swab without warning.....READ EXPENSIVE!

Now you need to check with your manual on how to lock up the camera's mirror for cleaning mode.
Remove the lens with the camera switced off (something you should always do anyway because the CPF attracts dust if there is power on).
Switch the power back on, lock up the mirror and leave the power on. If you need to put the camera down place it with the open lens mount facing down.
If there's not too much dirt the first method of cleaning is a good blast of air from a good quality puffer ....the Giottos Rocket Blower comes recommended. Canned air does not. Hold the camera above your head and blow air in from below so that any dust falls out. Swithch camera off, reattach lens and go take another picture of the sky at f22. Download the picture, blow up 100% and compare with the first one.

If that's not done the trick it's time for a wet clean with a sterile sensor swab and Eclipse fluid. This is well descibed in the attached article so I don't need to go over it again. This can be a bit fickle and sometimes it takes 2 or 3 shots to get rid of all of the dirt. One swab for each attempt

Cheapest place I've found for Sensor Swabs and Eclipse fluid is Surrey Photographic...there's a website and they have an Ebay shop too. Be sure and order the correct size swabs for your camera.

I'm using my camera fairly intensively and so far have only done a wet clean once every 6 months or so....so it's not someting you need to do a lot.