Try them on with the appropriate socks. The best time to try on new shoes is at the end of the day when your feet are 50% wider.
Always fit your larger foot. For most people, the larger foot is the opposite from the hand they use to write.
Stand up in your shoes. Walk around a bit. You should be able to wiggle your toes in the front of the shoe. You should have 3/8" to 1/2" of space between your longest toe and the end of the shoe.
Don't buy shoes that are too tight. If you are hoping they will stretch to be comfortable, they probably won't. It is true that soft leather and suede will give slightly, molding to your foot; but they will not dramatically increase in width. There is a difference between a "snug", comfortable fit, and a "tight", uncomfortable fit. A few laps around a carpeted room should help you decide how you feel.
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