Simplify Your Direct Mail Message
Postcards are small and direct. That's an advantage they have over a direct mail letter. With no envelope to get between you and your recipient, the message can make an immediate connection.
"Immediate" is the key word here. Limit your postcard to one main idea, and keep your language clear and simple. That doesn't mean you should talk down to your audience. It just means you should make your message and your offer so clear that readers "get it" upon first glance.
When you confuse a reader, you lose a reader. So make your message clear.
-Brandon from PostcardSmart.com