It try to not let it happen, but it still gets me every now and then. A few items in the camera case help once you are on location, hiking or using the gear. One is a good boars bristle shaving brush. I brush stuff off with the bristles and tap the camera a few times as well while holding it up. This gentle tapping dislodges dirt particles I can see fall out.
Canned air seems to blow it into the cracks.
A damp cloth helps here, usually a bandanna I would wear anyway. When I can, during our travels, I hit a car wash. It also makes the traveling easier as I feel cleaner. This has to have a beneficial effect on my shooting. I find that protecting gear pays off big time in fewer images lost to dusty damage.