The dialogue of your story will probably be what your readers remember the most. It is the chief way to reveal the heart of the characters, a vivid way to show off the setting, and key to setting up the action sequences. That is why you want to make sure that it is interesting and properly utilized. Many books I have read failed at this because either:
1) The dialogue was full of cliches
2) There wasn't enough of it
3) There was too much of it
4) It was absurd/unbelievable/gross
So what is the solution to avoiding those pitfalls. Basically, do the opposite of what was described above.
1) Use original and vivid dialogue. If you are writing sci-fi/fantasy, really work hard at creating slang to expand and grow your reader's mind and imagination. If you are writing realistic/historical fiction, you have a tougher job to do, but try to utilize the lesser known dialects of the place you are writing about for some local flavor.
2) Use enough of the dialogue to keep the story moving. If no one has said anything for two pages and the setting has been described all the way down to how the light glimmers off the wings of the fly eating the protagonist's cheesecake, it's time to ditch the awkward pause and make the characters say something.
3) At the same time, don't bore the reader witless with a character who is a blabbermouth, blowhard, or chatterbox. In particular, if you are ramming a worldview down someone's throat (even if it's a Christian worldview), you are asking to be thrown into the trash can. Use pointed, insightful words to get your point across and don't beat your subjects to death. If you need to use a Mongol warrior or car chase to knock your protagonist off their high horse so you can move the story forward, so be it.
4) Be tasteful. Don't throw in the foulest, grossest words you can think of just to shock your reader. Those who are decent human beings will eventually toss your book (and lose their lunch) and those who aren't will get bored once they get their cheap thrill and move on to the next perverted book. Neither will be likely to return to read your story again. Think of it this way: who gets married in the end? The fun, kind, interesting, and decent girl, or the floozie who is drunk and strung out on drugs all the time? The hardworking, adventurous, ambitious young man with a career and a house or the bad boy who is always in and out of jail (and his mother's house)? Just like dating, readers ultimately always want the book that is enjoyable and has a good heart. So ditch the leather jacket and the tube top and wear a dress shirt or a nice blouse for a change, eh? Keep your dialogue clean and fun.
