Or, up the ante like I do and HOLD DOWN THE SHIFT KEY! (It's been a boring day in agencyland.)
This will all make sense after Cal's question: When writing a spec, how closely should the formatting resemble produced scripts from the show you're writng? I ask because I'm following a produced script very closely, so my spec includes lots of capitalized of sounds, fragmented action description, and other language particular to that show.
Capitalized sounds and fragmented action description are actually very common in all scripts. Scripts are not written like novels; they are often choppy. Many writers think in shots, and write exactly what they want you to picture in each frame. I did once read a script that had NO complex sentences and it kinda drove me crazy...but used well, fragments are 100% okay. Your instinct to follow the show's real script is a good one - but remember that shows have many different writers, so while one script may use lots of fragments, another episode might be completely complete sentences. Every writer has a different style.
As for the caps (or shift), some things you always capitalize, like slug lines and names of characters we're just meeting. Beyond that, it's customary to capitalize anything you want to emphasize, whether it's an object your character picks up, or a big moment in the story. I think there's a line in the Fringe script like "AND THEN THE WHOLE THING FUCKING EXPLODES." Or something like that. It ups the intensity. It can also help establish your tone. Are you capitalizing phrases like BULLETS SPRAY INTO THE CROWD or HE CHUGS THE ENTIRE BEER, THEN GRABS ANOTHER? What you consider a BIG DEAL in your script will give us a sense of the world we're in.
Of course, don't get carried away. You don't want your readers to feel like they're being yelled at.