Different sunglasses look better on different faces. Sure, you could try them all out until you find one that works, but if you need a little help, here's an infographic that will help narrow it down for you.
It's simple: first, you determine your face shape by tracing it in a mirror and comparing it to the shapes on the infographic. Then refer to the second half, which lists your face shape and the sunglass styles that match. It even explains why those sunglasses are a good fit for you, which is good to remember if you're ever out without the guide on hand.
With that, you've narrowed it down from way too many options to just a handful, which makes this process a lot easier. The Sun Authority also has an interactive guide at the link below, so check that out as well if you're interested.
Choosing the Best Sunglasses for Your Face Shape [The Sun Authority]