Take your characters to lunch
Yes — literally. Go to a restaurant. Order food. Pull out your journal. Have a conversation with your character. Pretend that you’re meeting them there for lunch like you would a friend of yours. Ask them questions like, “What are you going to have?” and “Is it just me, or are those people talking way too loud?” Your characters’ responses may surprise you and open up new doors to their personalities. I only started doing this about 3 years ago, but I do have to say, my characters have become much more dimensional and unique since I started.
Talk to yourself
And I’m not just talking about reciting lines of dialog from your story. No, no. I mean full-on talking to yourself. This might sound really strange, but it works. If you’re new to this, try doing a monologue you want to include your screenplay. Don’t write it out, just say it. I cannot count how many times I’ve stumbled upon a great piece of dialog by doing this. Does trying this make you a weirdo? Yes. Should that stop you? Heck nope. Also — do accents. That’s how I came up with a villainous frenchman once, so try it.
Do bizarre things that make you embarrassed of yourself
This is probably one of my favorite things to do to help my creativity — and it’s simple. The title says it all. If you’re stuck on a scene — it’s not flowing well and the dialog feels contrived, then I suggest sitting in your bathtub for a while. Perhaps you should wear wigs and costumes when you’re stumped. I do interpretive dance (ironically,) practice my draw with toy revolvers, sing songs from HMS Pinafore and The Mikado (do I love comic operas or what?) — anything that jump starts my brain creatively is alright by me — even becoming El Espadachín while I write in my office (as demonstrated below.)