I really like:
Think Like Your Customer http://www.amazon.com/Think-Like-Your-Customer-Understanding/dp/0071441883
You can learn how to craft your messages from books, but the real answer to your question is to ditch the books and go to your existing customers and ask them:
- Why did you buy?
- What value do you get from what you bought?
When you have the answers to those questions you can then craft a script that goes to solving someone's problem, not pitching a product.