If the first rule of email newsletters is "Drive Interest," the second rule is "Interests Change." Despite all your efforts to write compelling and focused newsletters, there will come a time when most readers will move the cursor over "Click here to unsubscribe." Be prepared for such a move by giving them other options on the unsubscribe page. Options can include a reduced frequency -- perhaps a monthly compilation is easier for them to cope with -- or a choice of your other newsletters. In addition, always place relevant offers on that page. It might just be your last opportunity to monetize that customer!
Next: Bonus step!