Lots of great pointers here. I shoot a lot of outdoor editorial in varying conditions so I'll add my two cents:
I try to minimize the amount of time my sensor/mirror is exposed by prepping everything else first, i.e. lens caps, rear caps.
Use your strap and orient the camera facing down whenever you switch. Dust and debris can still float up into the body, but if it's facing down you eliminate straight on debris carried by wind, hair and sweat from your own body, exhaust grime carried by winds, etc.
Don't remove the first lens until you have the second lens ready to hot-swap with the rear cap off. Then just play Indiana Jones and put the new lens over the hole as soon as you remove the old lens. Once the new lens is secure, worry about getting the rear cap on the old lens, taking the front cap off the old lens, etc.
Basically just streamline your process so you don't wind up with your hands full fumbling with a lens cap while your body sits face-up in a dust storm.
Like others have said, my main objective in the field is to avoid switching lenses if at all possible by keeping a short and a telephoto body on hand. I don't have a lot of gear but I will just use a rebel for telephoto if I'm running short. I'd rather focus+recompose and eschew the framerate etc than mess with lenses in a chaotic situation and potentially be out a few grand for repairs.