You don't necessarily have to date "below average" women, but you do need to be at least somewhat realistic. If you want to approach a super hot chick, go for it, but you have to have something of "equal value" in return. Be that the best personality she's ever experienced, or what have you - you have to be able to offer just as much as the person you want.
There is no such thing a below average looking ! Beauty is in the eye of the beholder my friend, you may think yourself to be 'below average' but many girls out there would think you to be gorgeous. It all comes down to personal preference, find someone you click with and Who has an amazing personality and looks will take a backseat.
Girls date for personality and guys date for looks. This is because women are seen as objects so this is why you often see prettier girls with not-as-cute guys because the girl likes the guy for who they are. Maybe try dating girls for personality and get to know girls you usually wouldn't go for simply because of her looks. Dating within your league would be easier to succeed though. That is always something to remember.