1. Know your characters. Once you decide on the story your want to write, spend time getting to know your characters. Not just the color of their eyes, or the type of dress they wear – but how they think. How they would react to any given situation. Think of people you know, pick out various characteristics and ascribe them to the characters. Let your characters have flaws; it makes them all the more lovable.
2. After you’ve written a scene with a fair amount of dialogue, read it aloud. If the dialogue doesn’t sound authentic to your ear, it won’t be authentic to the reader either. If you stumble over passages, consider rewriting them. Most times the stumbling is because you have too many words hooked together. When speaking to one another real life people seldom use the King’s English. They speak in fragments, and use contractions. If your dialogue sounds lumpy, try paring it down. Sometimes less really is more.