Read the whole questionnaire first
Check how long it is and what it asks for, then agree a deadline instead of promising a quick answer.
Answer from facts you can show
Describe what you do today. Do not claim certifications or controls you do not have.
Keep a library of answers
Save approved answers on hosting, access, backups and data handling so the next one is quicker.
Get the right person to review
Have whoever runs your infrastructure check technical answers before you send them.
Say what you will do next
If a control is missing, say if it is planned. Honest gaps build more trust than overstated answers.