This step might be difficult to implement depending on how large your list has grown. Still, when somebody joins your list or purchases from you it really helps to send personalized email. This shows that you are there ready to help them in any way you can. You can even hire this portion out, but the results will be well worth the effort. This will greatly cut down on unsubscribes and greatly increase your profits.
If you're using a service like Aweber, it's easy to do.