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.
Create content that's relevant to your business but not blatant advertising and your readers will naturally start to think of you first when they need your type of services in the future. Topics can include things such as how-to's, sharing new developments in your line of work that may be useful for readers to know, monthly contests, featured clients, or case studies; people love to see photos of themselves or read about themselves, so featuring a client is a surefire way to get them to forward your newsletter to their friends. How many restaurants have you been in that hang newspaper articles about themselves on the wall? Same concept, just using a different media.
Use photos and images to spice things up, and keep things short; after all, none of us have enough time and we like things quick and to the point. Enough said.