Recently I started reading Web Analytics 2.0: The Art of Online Accountability and Science of Customer Centricity and had my eyes opened. For at least 5 years I have been using GA but was barely scratching the surface of what it had to offer. Then WA 2.0 introduced me to Segmentation which is to process of breaking down user activities by various actions. For example if I only want to see what traffic to a blog is going I can create a segment that only looks at traffic going to http://www.mywebsite.com/blog and from there I can analyze just Blog Traffic for things like keywords, most popular landing page, etc. I cannot recommend this book enough, go and get it now! (Disclamer on the link above: If you buy via that link I may make a nickel or two.)
Another GA topic I was recently introduced to is Alerts. In GA you can create Alerts to shoot you an email when various things happen on your website. Things like: surge in traffic, drop in traffic, drop in Google traffic, etc. This allows you to stay focused on new things while having a nice safety net in place in case things go wrong. A great article from Rebecca Lehmann on SEOMoz last Month gives you 7 excellent alerts and super easy links to add them to your GA account with.
How about you? Do you have any special secrets that everyone else should be using for Google Analytics?