Well, you can spend hours and hours writing and editing and laboring over a great sales letter, but your time will be wasted if your prospect doesn't open it. My advice to you is to avoid gimmicks. Don't use labels. They receive a nickel for each addressed envelope. Don't use a postage meter.
Stamped mail is likely to get opened faster than metered mail.
If you want to attract a lot of attention, use three or four stamps instead of one 32 cent stamp. If you're going after four or five prime prospects, you might try sending your materials to them by Priority Mail or FedX, and put it in the appropriate envelope or pak. And don't forget follow-up. I've seen good direct mail campaigns that have cost five figures sink quickly at this point, because their users weren't foresighted enough to prepare to deal with incoming leads promptly and efficiently. You're welcome to print out a copy of this article for your own personal use, or to send to a friend.