I've analyzed thousands of surveys over the years. Here are the 5 mistakes I see constantly:

1. Too many questions. After question 10, completion rates drop by 50%. Keep it under 8 questions.

2. Leading questions. "Don't you agree that our product is amazing?" — this gives you useless data. Use neutral phrasing.

3. No mobile optimization. 70% of survey responses come from phones. If your survey looks bad on mobile, you're losing 2/3 of your data.

4. Double-barreled questions. "How satisfied are you with our price and quality?" — that's two questions. Split them.

5. No incentive. Even a small reward (discount code, entry into a raffle) can 3x your response rate.

I built PollCraft to solve all of these. Every template follows these principles by default.