Explain benefits clearly. Keep it short. Some years ago I used to write long selling-letters for clients. And the long stuff pulled just great. Now, things are changing.
Readers are less patient.
Their attention spans are shorter. Which means that the sales letters, e-mail, etc. Keep it lively. Hey, it isn't a crime yet in this country to have a little enthusiasm or a sense of humor. If your marketing materials are flat or boring, bring a little personality to the party.