Seriously, if you want to get sick, don't pay any attention to the secrets I'm about to disclose to you...
1) Don't touch anything or anyone. Not with your fingers, not with you clothes, not with your right kneecap. The only thing that should be touching anything is the bottoms of your shoes. Hopefully, somebody else will be going to your floor, but it might mean riding for a while until the the elevator decides to stop on your floor. Unless you are forced to perform CPR on somebody, don't touch anyone!
2) Don't ride with little children. I love kids, but they're germ magnets. If you see a child on the elevator, don't get on. If you are on and a child gets on, get off immediately. Unless you have your own children with you, and they're too scared to ride in a separate elevator without you, don't ride with little children!
3) Wear lots of layers. Just in case you do touch something/someone, or something/someone touches you, you still have a defense. By wearing layers, you can remove the contaminated layer and burn it in a trashcan (most elevators have trashcans nearby). The more rides you planning on taking on the elevator, the more layers you'll need to wear. Unless you are going to ride naked and shower immediately upon exiting the elevator (which seems just a little extreme to me), wear lots of layers.
4) Don't Breathe. Hold your breath. Even if you're not touching a thing, you still must hold your breath the entire time to completely avoid exposure. If you can't make it all the way to your floor, get out, refuel, and then get back in. Or, you can wear an oxygen tank. Unless you're about to pass out and be forced to touch something or have somebody perform CPR on you, don't breath!
No need to thank me.