How To Write a Powerful Call-to-Action

In this article Constant Contact's Amy Black provides these tips on how to get your readers to take action when they receive your emails:

Know exactly what you want them to do. If you don’t know what you want the reader to do, they certainly won’t know. Do you want them to:

Buy something?
Sign up for a service?
Read an article or get more information?
Visit your website or store?
Make an appointment?
Make your call-to-action:

Visible – If your CTA is buried in the middle of a lot of copy or only found at the very bottom of your email, your reader may not see it. Your best bet is to include your CTA in a number of places in your email—right up top, somewhere in the middle, and at the end.
Clear – If your reader is unclear about what you are asking them to do, they aren’t going to do it. Have a friend or colleague read over the offer to make sure it’s easy to understand.
Compelling – Put the benefits right up front and show and tell why this is an offer they can’t refuse! Also, use action-oriented phrases like "buy now" and "call today."
Urgent – Give your readers a certain time period in which they have to respond. Setting a deadline is a proven way to boost response.
Repeat the offer on the webpage you link to. This tip is mostly for people who want a reader to purchase, or sign up for, something. For starters, link directly to the page where the reader can take the action you’ve asked them to take. When they get to the page, make it easy for them to remember what you are asking them to do by repeating your call to action.