Tips for Writing Questions
Make sure the language is natural (i.e. how people talk). Phrase questions the way a person would ask them verbally, keeping it short and simple.
Your users will have the greatest success getting the answer they are looking for if you provide as many variants to the question as possible as everyone will phrase things differently. For example...
Draft one question at a time.
Tips for Writing Answers
Answers should be short, specifically for voice channels (2-3 sentences max.), but more than a simple "yes" or "no" answer.
General Tips
For voice channels specifically, use a comma for short pauses between words and a period for a slightly longer pause.
Try to avoid symbols that the voice channels won't know how to translate and use actual words instead.