With Google Analytics there are hundreds of metrics you can look at, and although all are important, there are seven that you should focus on:
Location: Audience > Overview
Knowing how many visitors your site has is important. It tells you if your marketing is working, what days of the week you get more visits, etc. You can also see how many unique visitors you are getting, and from there drill down and see how many people are coming back to your site more than once. Depending on your site return visitors may be very important, so it’s important to know if your site is giving them a reason to come back.