Ibsen used to say, about writing plays, that in the first draft your characters are strangers. In the second draft they are friends, and by the third they are close family.
– Charles Harris, from 9 Steps to Writing Dialogue with Rich Subtext.
Charles Harris has a lovely piece on writing dialogue that has subtext. I always liked my dialog, so I’m going to have to try his guidance on and see if I can add some more depth! The quote above really inspired me.