I think to write well an author needs to be empathetic. Maybe not in real life but he/she needs to empathize with those poor characters he's created. When that's achieved it's very easy to breath life into their actions and words. They become believable because the writer knows them well and knows what they'll do, how they'll react, what they'll feel and what they'll say in a given situation. A good way to practice is sit in a very public place, listen in on other's conversations and then make up the story that should go along with your victi... I mean subject.
Mad