When I develop an Email Marketing strategy I often look at these five things in order to truly assess how developed the strategy currently is, and where it needs to go. These are the five things I look for:
You'll hardly ever want to send one email to all of your clients. A good email manager will have their email list segmented in many different ways so that you can make sure the right client views the right message. A message sent to everyone on your list may get a lot of attention, but the more sophisticated your strategy becomes the more diversified it is. I once met with a company that had a 14 tier Email Marketing strategy. They had identified 14 uniquely different emails they could send to different parts of their client base for marketing purposes. It doesn't have to be 14, but really think about the people on your list, are they interested in everything you have to say or only parts?
Most Email marketing platforms allow you to personalize your messages. Typically the people who've signed up on your lists have given you their names - use them. "Hey Andy" sounds much better than "Dear Reader". You will want to make your reader feel as though this message is a personal connection with them. Not to necessarily trick them, but to help them feel as though there is someone out their concerned about their needs and a has willingness to fulfill them.
Make sure that you use HTML templates when sending your emails, plain text is too easily overlooked. Using an HTML template will allow you to use graphics, colors and style very similarly to a simple webpage. You only have a split second to capture a reader's attention after they open your message. You may even want to hire out some custom design work to get a look and feel for your templates. Test different templates to get a better feel for engagement.
Give consistent updates to your readers, whether its every Tuesday, or the first business day of the month. Give your readers something to expect. The more consistent your messages become the more real engagement you'll receive.
This probably deserves more fore thought than anything else, connect what people are reading in your Email Marketing messages to other areas of your businesses marketing efforts. Use similar graphics on the website, or print pieces. Give people more than one opportunity to view your marketing pieces through other mediums (mailers, advertisements, etc.)