Face it, we're all bombarded with too much information today and the last thing we want to do is read more of it - UNLESS there's something in it for us! If you want to make sure that your subscribers read your newsletters, and maybe even pass them along to their friends, you should concentrate on providing helpful or fun information rather than dragging on about your company and how great it is - BORING!
Newsletters aren't so much about promotion as they are about creating and maintaining relationships with your customers. By providing helpful or fun content, you'll make your readers look forward to the next issue rather than just deleting it unread from their inbox - or worse yet, unsubscribing themselves from the newsletter. Which brings me to another point: your newsletter should always include an Unsubscribe link; not only is it rude not to do so, it's actually illegal.