Drama class never consisted of note taking, but the things I do remember apply to writing in very useful ways:
This refers to every movement made by an actor on stage. For an actor, this can be as hard to memorize as the lines. The margins of a script are never big enough to fit all the notes a director gives an actor. Then, the actor must make it all look natural instead of rehearsed a million times.
Each movement made by a character MUST have a purpose to it. But a character that doesn't move at all appears unnatural and stiff. The most common blocking purpose is to facilitate the scene (moves to door in response to the doorbell ringing). The more uncommon are propelled by emotion (pacing impatiently) or can be a character trait (moves to the table and runs a finger along the top for dust- character is a clean freak). The balance between dialogue and blocking must be made to keep the scene natural. And when you add more than one character to the stage, you must balance the blocking between them.
See how writing plays in yet?
This is a no-brainer. Even for those that have never set a foot in a theatre (though if you've never been in one for a live performance, I slap your cheek with a white glove and say 'get thee hither, man!') you know all about characters.
The difference is this: writing from inside the character's head, to actually embodying them. One particular drama class comes to mind, when our Drama teacher taught us the differences in how people walk. Some lead with their belly, some with their nose, some with their chests, and some with their toes... forehead... etc.
There are times when a scene jumps into my head so fast, my fingers aren't fast enough to get it down before the magic passes. Sometimes it's just one layer of the scene that hits me (like just the dialogue, but not the blocking). In either case, I whip out my trusty pen and paper and jot it down, script style. I'll include a short example out of my notebook to show you what it would look like:
Cole: (pulls Lesser by his hair and pulls him up to half sitting) You'd better start talking
Lesser: What would you like to chat about, sweetheart?
C: There was a woman you took from the apartment. What happened to her?
L: We took 4 women. You'll have to be more specific.
C: She would've been more scared than the others.
L: Oh, you mean bear-slippers-and-a-bathrobe? Ugh, that lady wouldn't stop screaming.
C: (lights L on fire and watches him writhe)
L: (mocking) Your Daddy's fire is a lot worse than yours.
Then I can go to my keyboard and put it in with all the punctuation and proper blocking, etc.
Hope this helps. Break a... pen :)