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2. Be careful not to overuse character's names.
3. Especially in conversations with more than two people, is it always clear who is saying what?
4. Do your characters speak their thoughts? Most people don't. And not all people mean what they say or say what they mean.
5. Keep dialogue tags simple and don't overuse them. Use said or asked. Limit the use of explained, demanded, complained, yelled, etc. If someone is explaining something, it should be obvious they are. The reader won't need to be told that so-and-so explained it. Use the words of your dialogue to show that they are demanding or complaining or yelling. Make your dialogue strong enough to stand on its own.
6. When possible, use an action tag instead of a dialogue tag. For example: "I'm going to walk the dog," he said, picking up the leash. becomes "I'm going to walk the dog." He picked up the leash. (Simple example, I know, but hopefully you know what I mean.)
7. Eliminate small talk and filler words such as how are you? so, like, um, well...