Consider the following:
It should not be too natural
If you listen to a conversation and transcribe it you’ll soon realise that people often go round in circles, they insert a lot of small talk and sometimes it’s even that two parallel monologues take place rather than an actual conversation.
It should only say important things
So, you actually need to condense it to what is actually about. It must have a purpose.
It should differentiate characters' voices
Each speech must be in the voice of the character that is speaking. Always consider: would your character say such things or use words like that? If you printed your section of dialogue and cut it up would you or anybody else be able to work out who says what?
When angry, becomes childish
Oh yes. This happens to the best of us.
It should take 2/3 of popular book
This isn’t of course a hard and fast rule. But it may be a useful tool for checking that you have enough dialogue in your book. It may also help you to identify where you are telling instead of showing. Dialogue is very much part of showing.
It should convey mood, character, reaction
Look at every single piece of dialogue. Is it doing all of the things?
Every speech should give information
Again check to see if your dialogue is doing this. Is it pushing the plot forward? It’s great also if your dialogue can multitask
Is it set out correctly?
The easiest way to check this is to have a book by reputable author and publisher open at your side. See how they’ve done it.
Take care with how you tag dialogue
Can you actually avoid tagging it at all? Often with an exchange of just two people you don’t need to tag. If you have the voice right for each character you may not need to tag. However, if the dialogue goes on for a page or more, there are more than two speakers, or if you are writing for young readers you may need to remind the reader who is saying what. Hopefully each speaker’s voice will be very clear. You can add a little body language if you wish. If none of this is effective and you really have to use a tag word use “said”. The readers will hardly notice it. At a push you can use asked, shouted or whispered.
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