Never use dialogue to expose story. Use short sentences to show how the characters speak, but only when it's necessary.

Short stories can have up to 20% dialogue, but it's best used to break up narrative and description.

Keep raising the stakes and adding conflict. Show how what the characters are saying is different from their real thoughts or feelings.

e.g. Don't offer answers to questions.

NOT - "How was your day, Jimmy?" "Fine, I guess."

BUT THIS - "How was your day, Jimmy?" "What do you care?"