How to Write Realistic Dialogue
One of the things I come across most often when I edit fics for the zine or beta them for other people is superfluous dialogue--anything that doesn't further the plot or develop the characters. This article gives great examples. Yes sometimes it's hard to cut something you wanted, but once you see it put this way, you understand why it's better for your story.
ETA: the obvous exception to people not talking in perfectly-formed, grammatically correct sentences: T'Pol. Again this is part of character development, and part of that other link about dialogue tags. Having T'Pol's sentences contrast with other people's in this way is a great way to let the reader know who's talking without repetitive or purple tags.
