There's an easy way to do screen protectors without getting crap under them.
(1) It's best to work in an area that has no drafts or breeze. Turn off fans and close windows and let the dust settle in your workspace for a little bit.
(2) Wash your hands.
(3) WASH YOUR HANDS!
(4) Dry hands thoroughly.
(5) Assess how the pieces fit without removing any film from them.
(6) Clean the screen with a lint-free cloth.
(7) Skinomi and Zagg come with solution. Spray your fingertips and the protector after peeling the protective film off. If it's one of the stiffer ones that doesn't come with solution only peel back about a half inch or so from the top of the screen side.
(8) Starting at the top, line it up with the speaker hole and the top of the device.
(9) For Skinomi and Zagg, just roll it down, you can adjust the piece after it's down if it's still wet.
(10) For the stiff kind, after you're lined up with the top, peel the film away while sliding a card down the protector. It's easier than it sounds.
Here is a video showing what I'm talking about. Don't flame me cause it's an iPhone. I don't care about that, only the technique.
I installed thousands of screen protectors when I worked for Geek Squad. Following these techniques I was the best person on both shifts in the entire store at installing screen protectors. You too can install them perfectly, every time, doing it like this.