1. Written survey - you will mail your clients a copy along with a cover letter, praising them for being your best customers and asking for their help. This is probably the slowest method — but also the cheapest.
2. Telephone survey - you will have a staff member call up and ask your clients the questions.
3. On-site / In-office survey - You have an opportunity to not even spend a stamp or a phone call by getting clients to fill out your survey when you see them or when they come in for their visits.
If you can offer a free gift your results will increase.
Also if mailing, enclose a postage-paid return envelope.
Make it easy for clients to send back their comments.