Don't:- Use any other tag other than 'said'. Well okay every now and then you can throw in a 'replied' or 'asked' but make sure it's only sparingly. Kind of like that book about the boy who ignores the vet's advice about feeding his fish "just a pinch and no more" and ends up with a fish bigger than Moby Dick........soooooo unless you want your ms harpooned, follow the advice above.
- Add any -ly words after the dialogue tag 'said'. You're writing a novel, not a screenplay so you don't need to tell your actors how to say the line. So no 'said adoringly'. No 'said grumpily'. No 'said quietly'. Not even 'said slowly'. Nothing. Just 'said'. Apparently the human brain just skips over the word 'said' without really registering it but if you add an adverb then it makes the brain stumble. Here is where you go off and read more about showing not telling..........
Back again? Great.
Do- Find your primary school teacher who taught you to find 65 different ways of saying 'said' because "repeating 'said' over and over again would just be boring" and "make sure to include lots of adverbs because they make a story much more interesting" and repeated that advice so many times that it became an ingrained habit that is almost impossible to break and when you find that teacher, slap them.
- Resist the above urge if that same teacher was the one to teach you how to write the mechanics of dialogue correctly. That is, using " " instead of ' ' and knowing when to use a comma, a full stop (period), and other punctuation marks correctly. Instead, kiss them. Knowing how to punctuate properly is a skill to be rightfully proud of. If it's something that you have to learn.......well then I think you should be able to slap your teacher twice.
- Make sure your dialogue is realistic. There are lots of exercises you can do: like transcribing a small segment of dialogue from a sitcom you've taped. (I say sitcom because they always have lots of dialogue but you could use any show really). Look at the pauses, the interruptions, the hanging endings, the language etc. Analyse a scene containing dialogue in a book that you think works really well. Why does it work? What parts of it stand out to you? Did you notice anything during a second or third reading that you didn't notice the first time? Do the same for a scene you think stinks.
- Read your dialogue out loud (or if you're much braver than me, ask some friends to do it in front of you). How does it sound? Is it realistic? Is it stilted? Does it flow smoothly? Is the language appropriate for the age/gender/background of your character?
These are just a few pearls of wisdom from the oyster I call my brain. Not a definitive list, you understand, just a selection for your enjoyment. An amuse bouche, if you will :)