Be an actor.
A few hours ago I realized exactly how necessary it is to get inside the skin of my characters while I'm writing them. I can't stop thinking in their heads, or hearing their voices in my ears--even for one second. Why? I can't make a character real if they aren't real to me. I think the most important thing earlier was to quit writing for a little while, close my eyes, and picture my character doing something. I closed my eyes for a whole fifteen minutes. I studied everything bout my MC and how she interacted with the possible love interest. I re-briefed myself in her shape, movement, and mannerisms. Then, I opened my eyes and started writing.
Man, was I on fire.
And, you know what else? I had to re-write an entire argument because I realized she caved way too easily. Totally out of character for a stubborn con artist.