Those with an oval shape are the luckiest of all! Your face will have cheekbones higher than the middle of your face, and your chin will be a bit narrower than your forehead, though not by much. Why are you luckiest, you ask? Because most -- pretty much all -- frames will look great on you.
You might want to avoid significantly rounded frames, as the general rule is to go for the opposite of your shape. Upswept corners will emphasize your cheekbones and make your jaw appear thinner and more angular.