Dialogue is not conversation. Conversation is two people exchanging information. Dialogue is two people in conflict — even if they are smiling.
Every line of dialogue should do at least one of three things: reveal character, advance plot, or build tension. Cut any line that does none of these. The most powerful technique in dialogue is subtext: your characters should almost never say exactly what they mean.
'I'm fine' means 'I am breaking.' 'Do whatever you want' means 'please stop me.' The silence between lines — the beats, the pauses, the actions — carry as much weight as the words. Read your dialogue aloud before publishing. If it sounds like you, it sounds like everyone.
If it sounds like your character, it is ready..