Dialogue, the multi-edged sword in a novelist's bag of tricks, hands down beats all the other techniques for the writing of living and breathing prose.  Dialogue can never "tell," it can only "show."  And what does it show?  Motivation, wit, humor, despair, anger, love, hate, and -- most of all -- personality!  Revising dialogue until every line sings is the most fun you'll have writing.  Blow a joke in your first draft, and have 'em howling by the end of your revisions.  Master dialogue and you're well on your way to mastering the craft of writing.