If you've got a round face, you'll be looking to sharpen those features.
Square and rectangular sunglasses are your go-to. They'll give a more angular look and help balance out your softer attributes!
And if you really want to mix things up, try out some asymmetrical sunnies. They'll give your face the contrast it's been craving.
MESSY TIP: Steer clear of round and dainty frames that draw attention to your rounded cheeks (unless ofc you're looking to bring out those baby-faced looks)