Another important point is every character should have unique dialogue. If I'm honest, many of my characters talk like I do in my first drafts. So, when I revise, I have to get rid of this. Ideally, each character's dialogue is so unique you wouldn't even need a dialogue tag. In a long work, I keep a cheat-sheet of slang or special unique words for each character. For example, one character might use a lot of single-syllable words, another might not use contractions. Good luck with your dialogue!
How about you? How do you deal with dialogue?