1. Educate in advance. Educate a lot. Why they need to respond, how easy it is, what the importance of the issue is. Doing it all at once much harder.
2. Always identify the sender. Your association acronym should be in every subject line so it's clear who it's from. This alone is continuously screwed up by organizations.
3. Use a return email that is known by users. The first occurrence of an email address should not be the Call to Action.
4. Tell them it's coming. Preferably a day or two in advance. Then when it arrives they'll recall it's what they were anticipating.
5. Activate the other messengers. If you have other communications vehicles -- be sure to use to inform Call to Action is out -- e-newsletters, MLS sign-on, web site, RSS, meetings, local presidents who will email others, legislative committee who will email others, asking company owners to send under their name (again, the known sender factor).
6. What's in it for me? If you aren't clear in both the Subject Line and the first two sentences what's in it for the end user, don't count on them to go much further. If promoting someone else's Call to Action (like national association), then you need to sell it your way -- and hope that works. Do not get overly technical or many will stop reading. The text of the email could still contain technical details, or a "for detailed information" link.
7. Tell them you're watching. Call to Action software exposes who does and does not respond. There's a degree of influence in saying - half of you responded, and we know who you are.
8. Do not use something goofy in the Subject Line. One organization used "Santa or Scrooge" as the start to a Call to Action message. Which meant we had to educate everyone to hunt it down in quarantine, spam, and recently deleted folders.
9. Do not use "spam" words and punctuation in Subject Lines that spam filters will trap -- like Alert, Urgent or multiple exclamation marks.
10. Consider engaging the public - ask your members to email their friends, families, clients, etc. Consider running print ads, radio ads, web placement. But if you send public to a site, make the domain short and easy to remember.
Any other tips that have worked for you?