Many rules can guide the writing of effective dialogue, but here are seven key principles that are often emphasized:

1. Make it sound natural: Dialogue is supposed to be something coming out from a real person and you should make it that way. Use contractions, slang, and other informal languages to make the dialogue sound more natural.
2. Keep it concise: Brief and to the point is how the dialogue should be. Avoid long, rambling speeches or monologues that don't advance the plot or reveal anything about the characters.
3. Use subtext: Good dialogue often has an underlying subtext that reveals something about the characters or the situation. Rather than stating things directly, characters may hint at their feelings or motivations through their words and actions.
4. Avoid exposition: Avoid using dialogue to explain things that the reader already knows or that can be shown through other means. Instead, use dialogue to reveal character, advance the plot, or create conflict.
5. Use dialect and accents sparingly : While dialect and accents can add flavor to dialogue, they can also be difficult to read and may distract the reader. Use them sparingly and be careful not to overdo them.
6. Give each character a unique voice: Each character should have a distinctive way of speaking that reflects their personality, background, and motivations. This can help readers distinguish between characters and make them feel more real.
7. Use tags and actions to clarify who is speaking: Use dialogue tags (e.g. "he said," "she asked") and actions to make it clear who is speaking. Avoid using too many adverbs or overly descriptive tags, which can be distracting.

And above are seven rules of dialogue that a dialogue editing service should be qualified enough to completely full filled. If you are determined to become someone who works in the industry or just wants to hire an expert to work with, these above rules will help you to choose the right one.