I'm currently reading The Eight Characters of Comedy by Scott Sedita. It's really a guide for actors on playing sitcom characters, but it's quite useful for comedy writers as well. Sedita mentions four "Cs." Commit is one of them. Actors have to commit to the role they're playing.
What's that mean? It's not about showing up early, and doing your research, and understanding the character, although you should do all those things as well. It's about to committing to being the character. Look at the GOLDEN GIRLS.
Rose is a complete idiot. Dorothy is sarcastic. Blanche is a manaholic. Sophia is mean.
They all commit to that characterisation. When Rose says something
idiotic, she can't act like it's idiotic. She has to be perfectly
serious. She has to think it makes sense. If she knows she's an idiot,
then it's not funny any more. Ditto, the others. Dorothy has to look at
the others like she really believes she's better than their company.
Blanche has to behave like sex is number 1 (and 2, 3,4 and 5) on her
list. And Sophia has to act like she doesn't give a damn about anybody
else or their feelings. The have to grab on to the role, commit and not
let go, not even for a second.
As I read, it occured to me that this is something I've been struggling with in my latest MS. The main character is supposed have a certain set of characteristics. She's supposed to be logical to the point that sometimes people think she's heartless. But she's not heartless. Deep down she feels just like the rest of us, maybe more. And I keep trying to highlight this with scenes that negate the characteristics I'm supposed to be establishing. Instead of seeming like X with a sprinkling of Y, she's coming across as rapid oscillation between the two. A wishy-washy version of what's supposed to be a really in-control character.
And it's because I don't commit.
But when you write you have to. You have to commit to the characters being who they are, even if they're bad, or not like you, or there's more below the surface. You have to commit to the plot, even if (and especially when) harsh things happen. You have to commit to the voice and the tone and the message and the setting.
That's not to say that there won't be little parts that are "out of character." It's just that if you want to go out of character, you have to establish the character first.