Cleaning the focusing screen is something that you'll have to do sooner or later. Dust not only gets onto the CCD, but can become lodged between the focusing screen and the LCD of the viewfinder. I take the view that pulling equipment apart for maintenance is standard procedure. But then again, I build my own engines, design my own microprocessor systems, and run over my own roadkill. How this will predict as to how successfully you will be able to clean your own camera's viewfinder, is anybody's guess.
Having said that, the procedure outlined below is what I do for myself, and if you follow the procedure and break something, then you're on your own, kiddo. If you're a klutz, don't take the camera apart - return it and take up painting instead, where you can't break anything expensive. There endeth the legal warnings.
1. Start by locating the locking clip, which is located on the leading edge of the mirror box.
2. With a pair of SURGICAL tweezers (strong, needle point, zero flex), get a firm grip on the clip, with the tweezers angled well away from the focusing screen.
3. Gently prise the clip away from the plastic retaining finger, and pull the clip slowly upwards.
4. Turn the camera right side up, and give it a gentle tap. The focusing screen and the spacer will simply drop out.
5. Invert the camera again and give the LCD a good clean. You can use pretty much anything you'd use for cleaning a normal lens with - I've even used cotton wool tips with isopropyl alcohol. It's not really critical, it's just a window, and the viewfinder doesn't have the critical resolution requirements of the CCD. Finish off with a good puff of a hand blower.
6. Using the tweezers, replace the spacer.
7. Give the focusing screen a good clean with a lens cloth, and blow off with a hand blower. The polarising tab locates on the left side of the housing in the photo below. You can't put it in any other way - so don't worry about which side (matte or shiny) faces the mirror. Replace the focusing screen and make sure it's seated properly.
8. Finally, press down on the edge of the locking clip very carefully (where the yellow arrow is shown). If you've got it right, the clip will slip under the black plastic retaining finger and lock into place. Don't forget to clean the mirror.
Before remounting the lens, give everything one final blow of air.