1. Try on shoes at the end of the day. Your feet typically swell during the day's activity and will be at their largest then.
2. A thumbnail's length of space in the toe box. Allows room for normal swelling and running downhill. The width should be snug but allow a bit of room for your foot to move without rubbing.
3. Know your running surface. Like tires, outsoles are designed to accommodate certain surfaces. Road running = choose shoes that are light, flexible, and cushion the feet. Trails = choose shoes that offer stability and traction with sturdy outsoles.
4. Replace every 400-500 miles of running (3-4 months for regular runners). Take a look at your pair of shoes and check if the midsoles and outsoles are compressed or worn. If they are, it may be time for a new pair.
5. Go to your local running store. Take your old pair to show the salesperson. The wear pattern on the bottom of the shoe will indicate if your feet are overpronated, underpronated, or neutral.
Try Valley Forge Running Company in Collegeville or North Wales Running Company in Phoenixville for proper fitting.