Dorothy L. Sayers, one of the great crime writers, was once asked by a man how she wrote such realistic dialogue between male characters. Did she have a big family or a lot of male friends?

Her answer was to the point:

I replied that I had coped with this difficult problem by making my men talk, as far as possible, like ordinary human beings. This aspect of the matter seemed to surprise the other speaker; he said no more, but took it away to chew it over. One of these days it may quite likely occur to him that women, as well as men, when left to themselves, talk very much like human beings also…

Sayers is being sarcastic, yet also true. Imagine what ordinary people sound like when you hear them speak. Then use that to inspire the sound and style of your dialogue.