You went to a shop, tried on a pair of shoes and you bought them. The next day you wore them and you got blisters. What detail did you miss when purchasing them? Here are simple rules for finding your perfect fit.1. The later, the better. Your feet swell to their largest size as blood pools in them by the end of the day, which makes this the best time to shop. Go too early, and you risk getting a pair that will be too tight.2. Get measured every time. Pregnancy, weight gain, and age can cause your feet to lengthen and broaden; your arches can change, too. Also, if one of your feet is bigger than the other (as is the case for lots of people), buy shoes in the size of the larger foot.For sports shoes, leave a finger’s width of space between the end of your longest toe and the end of the shoe for toe movement and thicker socks.3. Try them on. Sizes differ by brand (and even within the same brand). Ask the salesperson to bring your normal size as well as a half-size larger and smaller.4. Dress for success. Bring or wear the socks or hose you plan to pair with the shoes.5. Go with your gut. You will know within minutes if a shoe is right for you. If it is even a bit uncomfortable now, it will feel exponentially worse as time goes on.Seem Ram-Charitar, DPM, is a New York City–based podiatrist and the spokesperson for the American Podiatric Medical Association. She is a former model, too—and she really loves her shoes.