This is the one question that faces any Google Analytics user, new or more advanced. With the several dozen reports and variations that you can have where do you start? In answer, I would ask what are you looking for, what are the main objectives of the web site and what do you want to monitor. However, there are several web references that attempt to answer the first question, one is below which it outlines what and why you should be looking at these, such as: Audience location; Audience engagement; Mobile traffic; Traffic sources... does those fit your needs... read on:

http://www.natlawreview.com/article/10-google-analytics-categories-you-should-be-scrutinizing