A lot has been said about Dialogue. Don't expect to get it right during the first draft. I know I don't. First or Rough Drafts for me are getting the story down and I often found there are many problems with the dialogue. Not so many as there were when I began writing. I have a checklist of things I do when I'm in the revision stages of a manuscript.
!. Check each character's words forindividuality. Do they sound different from every other speaker?
2.Check each speech for emotional impact. Is the way someone says something have an impact on the reader and is it the one you want?
3. Make sure the characters words are in character. Do they show his social status, his education, his age and all the other things that make up his character?
4.Check the tag lines. Get rid of adverbs. Find ways to use action to identify the speaker.
5.Ask your self these questions. Does the dialogue help bring the character to life? Does the dialogue give the information a reader needs? And does the dialogue advance the plot? Is this bit of dialogue necessary or is it a throwaway? Does the internal dialogue serve the purpose you intend?