I've had a lovely long weekend, where I accomplished very little that I meant to, but relaxed and had fun and didn't get sick. This is what I mean, by the way, when I warn you that you won't have time when you think you will. I did get writing done, but not nearly as much as I meant to.
Don't repeat yourself. It's patronizing. Scenes and dialogue are there to serve multiple purposes, and regurgitating the exact same conversation kills whatever point it may have had the first time around. Your reader only needs that information once. If your readers are smart (and, if you want readers, you want the smart ones), they'll pick up on whatever you wanted them to see the first time the conversation happened.
If you must have a character relate the conversation within the narrative, please, for the love of all Muses, please summarize it. Mention the basic points, and nothing more. It is true that what a character gets out of a conversation is as telling as how they behave and speak within the narrative, but that purpose is served far better with internal dialogue than with the repetition of an entire conversation.
Another form of repetition that bothers me is when people describe characters or settings in the same terms every time it comes up. This is especially irritating when different perspective characters do it. I can bet you that my husband and I could write a two-paragraph description of our bedroom, and the only overlap would be in some of the nouns. We notice different things about it because we approach it differently, even though we're similar people living in the same shared space. Different characters noticing the same features about a person or landscape means that either that feature is grotesque, or that the characters are telepathic. If there's no precedent for telepathy, that tosses me right out of the narrative.
It's a lost opportunity when the same terms or aspects are harped upon every time someone or something comes up. Even the same people will notice something different depending on mood or where they're looking, and sticking to the tried-and-true descriptive terms cheats the readers of potential characterization or making the world more real to them. The only place where it's okay is in songs and epic poetry. If you're not writing one of those, knock it off. Break out your thesaurus, if you must, but find new words.
I can't say I don't repeat myself. It's a real problem in first and second drafts; by the time I'm getting toward the end of the draft, I'm not sure if I've already written in an important piece of information, so I just toss it in there as if I haven't. I discover upon my read-through edit, then, that an essential tidbit shows up two or three times, and I have to figure out which reveal is the most natural.
If I were anything but a pantster, I could avoid this by outlining where things are supposed to be shown to the reader. By now, though, I am nothing if not honest to myself. Finding the same bit of information sprinkled throughout my manuscript makes me laugh at myself, and edits should be fun on some level.