Many writers, like myself, are introverts and this can weaken our dialogue writing. Use everyday tasks to listen in on conversations: getting your car serviced, picking up the dry cleaning, shopping, etc., etc. No, not all talk will be interesting; let's face it, it is only pertinent to those involved. It's to get a better grasp on inflection, tone, and other aspects of speech and human interactions. Occasionally, you will hear some very colorful people who may inspire characters big or small, just so long as they move your story forward.