Oh how I love receiving Starbucks bonus stars! Just log in to your rewards account and head to your Account Home Page (Rewards Dashboard) and scroll to the bottom. If see an offer like the one shown below you are eligible to earn a bonus star.
Click on the "Start Now" button and follow the directions to complete the tasks (they are super simple and only take a minute). Then check your email and you should find a confirmation which will give you the link and instructions needed to enter your bonus star code.
Don't forget to get the Bargain Blessings toolbar to print coupons and stay up to date on all the latest deals!