You might consider making the language in your alt text actionable, such as "Click here to download the ultimate content creation kit." Actionable alt text will essentially turn every linked image into another CTA. So, even if someone doesn't see the snazzy GIF of my latest offer (or if they hover their mouse over an image that does show up), the alt text will beckon them to click.
Think about mobile. If a campaign doesn't show up on mobile devices, it's not going to perform very well. Everything you send should be mobile-friendly. Check out ReturnPath's "Email in Motion" infographic for some data that might affect the way you design your emails. One of the highlights: According to the study, 63 percent of Americans and 41 percent of Europeans would either close or delete an email that's not optimized for mobile. Might be time to start using a responsive template.
Think as well about the kinds of metrics you're evaluating. You probably know that interaction with email campaigns is measured through open and click-through rates. While it's meaningful to review email response in this way, if this is all you measure, you're missing the bigger picture of the value of email to your company and its customers. These rich metrics in the email are great. However, there is a distinction must be made between:

This article is by far one of the most interesting and fun articles that I have read in a long time. I say fun because the points mentioned here are simple and easy to read. They are not long passages that speak a lot and tends to lose focus. On the contrary the points mentioned here were in short crisp sentences that did not bore me but made my read a pleasurable one. Thanks!
Alternatively, at least, an eye-catching design. It’s worth letting a proper designer have a go at prettifying your emails. Customers are often opening emails on the go, so you need to work hard to grab their attention. Making your emails nice to look at is a brilliant way to hold their eye. Netflix put time and effort into making their emails stand out, personally and visually – and it pays off for them!