Warmachine,
I clean dust off by.........never letting the stuff get on a model in the first place!!
I know, I know........it's an imperfect world and we all don't have a hermetically sealed, climate controlled, Ph neutral showcase to display our wares. Wish I did.
But Mike has some good ideas....and to add to his ideas......I use Q-tips dipped in warm water, and take note, if you seal your decals with a clearcoat, you can (and I do) run your models (carefully) under the faucet if they're really grubby - provided the structure of the model is robust enough to live through the experience. A tiny foam make-up applicator can work wonders for this.
I also use my airbrush to blow dust off my models.
The main problem (you'll see when you try) is to remove the dust particles that have adhered to the model surface - creating a film - sorta like road grime on a car. It's easy enough to get rid of the loose dust - but what's next?
This grime must be washed off - it's the only way. That's where soft bristled brushes, Q-tips, little bits of flannel material come in handy, to actually scrub, or polish, the offending crap off your model.
Once that's done, if you don't plan on keeping them on display permanently, use large ziplock bags to place the model into, then place the model in a box - I use keyboard boxes - long and flat - perfect for cars.
Good luck!