Writing dialogue has some rules which are very essential to obey. The rules have been given below.
1.Think over the topic and arrange the ideas in a logical order.
2. Use contracted form.
3. Use minor and short sentence.
4. Use expression- thank you, sure, yes, oh god, excuse me etc.
5. The language should be colloquial and practicable.
6. The dialogue should be natural and rapid.
I have given you Madhyamik 2021 English Suggestion link. You can read and see the suggestion and download the PDF.