When writing dialogue, challenge yourself to let your characters speak for themselves, in any way they must.
Find ways to free yourself up. Write their words on paper using different pens for different characters – just as Aleksandr Solzhenitsyn used to do – the elegant fountain pen for one character, the chewed Bic for another.
After you’ve given your characters a chance to empty themselves, cut and trim, combine, or pick a line or two that says it all. Often what people really mean is not what they say. Look for that tension. And remember, what people don’t say is often far more powerful than what they do say.