Keep an eye on your stats. Most email newsletter services offer free reports that contain helpful information. Learn how to read and understand your reports, so you can use the stats to improve your campaigns going forward. Pay attention to your open and click rates, and identify any patterns that make those numbers go up or down. If a campaign receives a high number of unsubscribes, then try something different the next time.
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!