When I started working on my novel, I noticed that writing dialogue came naturally to me. Since the only writing I'd done for years was for theater, this made sense. But I soon noticed, flipping through my first draft, that the manuscript was mostly dialogue. It didn't look like a novel. It looked like...a script. Oops.
My sister said, "you're expecting the set people and the costume people and the lighting people to take care of everything else. But there are no set people and costume people and lighting people."
So I worked on adding description to break up the dialogue. Anyone who's ever taken an acting class is familiar with the concept of motivation. You read the lines, and figure out what the character wants from the person they're speaking to.
My novel is told in the first person, so I ended up with several variations of "I wanted him to..."
Not good. I needed action. This is where my theater background actually started to help me instead of hindering. I acted it out.
I would mentally put myself in the situation, say the lines of lovely dialogue I'd already written, and observe myself. Sometimes literally, in front of a mirror. But more often, I just noted what my physical impulses were, then wrote them down. I should note that it was at this point that I gave up on the idea of writing in coffee shops.
My training in Playback theater was especially helpful for this process. Playback is improv, but not the comedic type. We listen to stories and experiences offered by audience members, then we act them out on the spot. I've found that Playback helps me get into the heads of others by connecting to universal emotions instead of focusing on differences. I often have to play someone who is not my age, gender, race, etc. It's the kind of role I would never be cast in for traditional theater, but it happens all the time in Playback.
One time, I remember I was acting out a scene and I actually made myself physically ill. I got so upset that I felt nauseous. I had to stop and remind myself that not only was it "just a story," it was a story I freakin' made up!
What can I say? Actors are intense.