Watch the growth of your list. Is your email list growing or shrinking? If more people are unsubscribing than are registering to your list, it's a good sign that you need an entire strategic overhaul on your email policies. If there are a lot of people unsubscribing it could be because your content is not relevant to the people that you're sending it to. In this case, try to segment your list differently or change the type of content that's being delivered through your email blasts.
Email design matters in any successful email marketing campaign. If your emails look terrible, that reflects badly on you, and can make people stop reading. With more people than ever reading emails on mobile devices, it’s important to use a responsive email template so your email resizes automatically whether people are reading it on a phone, tablet, or desktop.