VERNACULAR: It's not as hard as it looks, really -- there are only a handful of specialized words that will appear in any script. Here they are:
#1. INT./EXT. In the scene heading, this designates indoors or outdoors. It gets a bit tricky, sometimes, when you're outside, say, underwater. Are you INT. LAKE or EXT. LAKE? You decide. And check out the screenplay for THE HUNT FOR RED OCTOBER for another stylistic choice -- it dispenses with the convention altogether.
#2. BEGIN CREDITS/END CREDITS Not necessary, but you can do it if you've consciously designed a credit sequence into your film.
#3. (V.O.) The abbreviation for 'voice over.' I prefer not to use it as a parenthetical, but place it next to the character's name. It implies a narrator, separate from the screen action.
#4. (O.S.) The abbreviation for 'off screen.' This is dialog coming from a character who is in the scene, but out of camera view.
#5. (cont'd) A particular parenthetical, used if a speech has been interrupted by description or a page break.
#6. CUT TO: Can be used between every scene, between major sequences, sporadically whenever it's appropriate to the rhythm of the script, or not at all. Particularly useful for manipulating the page count.