What you track and the reports you pay attention to within Google Analytics depends on the goals of your site. Google Analytics has over 80 reports, and only a small percentage of those reports provide truly relevant information and give value for your site. Every site has a unique set of goals based on the main function of the site, and these goals will help you to pick the reports that really matter for your specific website. If your site is a retail site, then one of your main goals might be to increase your conversion rate of visitors to customers from 1% to 2%. That might not sound like a big difference, but that would be a 100% increase in revenue!

To find out exactly what is important to you, here are some questions that will help narrow it down:

Here are some general interests based on the type of site, along with the applicable report from Google Analytics:
ECommerce Site: Sells products or services

Lead Generation Site: Creates and captures leads

Brand Awareness Site: Increases the product or brand awareness