You can add the instructions on how to claim the coupon right in your contest details on the main page and on your post participation page.
Also include them in the automatic email that sends out to people that claim it.
How to claim coupon:
- Do participants claim it in person at a physical location? What is the address?
- Are you sending them a digital good?
- Can they claim it online? What is your website? Where do they put the coupon code in on your website?