Break up the copy into smaller paragraphs and emphasize important points with under lines or handwritten notes. Including several pieces in a direct-mail package often improves response. Don't let the reader off the hook. Leave your readers with something to do, so they won't procrastinate. It's too easy to put off a decision.
Involvement is important.
Prod them to act now. Set a fixed period of time, like ten days. Or make only a limited supply available. Make it extremely easy for the reader to respond to your offer. But always ask for the order.