Conversations must hide instead of explain. Hide when you can reveal. Lie when you can tell the truth.
Allow your characters to misunderstand, to talk at cross purposes, to interrupt, to hesitate.
Direct the dialogue off stage. Call for the waiter to pay a bill, call to the bartender to order another beer. Allow the action to interrupt the flow.
Have your characters answer questions with questions. Like “Did you steal the picture?” with “What do you take me for?”
Allow your characters to talk to themselves. “What am I doing here?”
Just a few ideas to help you make your dialogue endlessly fascinating.