If you have flat feet, the one thing you need to guard against is over-pronation. For this, you need shoes with a deep heel cup as well as a midsole that is designed for pronation control. In fact, the shoe should also allow for your custom inserts or orthotics, if required. It is also important to remember that pronation causes the foot to widen, so a narrow toe box is absolutely avoidable. As a thumb rule it will help to keep in mind that if your feet are stiff, you need to look for adequate cushioning in the shoe, while if you have flexible feet, you need to look for shoes that provide adequate arch support.