Many sports injuries unnecessarily occur for two reasons: you use the wrong shoe for the activity or your shoes don't fit properly. Remember that your shoe size, whatever you ordinarily think it is, should not completely dictate what shoes you wear. A size 10 shoe from one manufacturer might fit you perfectly, while another size 10 shoe will be too small. What's most important is how the shoe feels on your foot.
It's best to try on shoes late in the day, because your feet swell over the course of a day. Wear socks of the same thickness as those you'll wear during your shoe's intended activity. Remember to check for width, too. If you have an extra-wide foot, get wide shoes. In North American sizing, the width of shoes is indicated by a letter or letters after the number (D, E and EEE are extra-wide sizes). Don't buy a shoe that's too long to make up for it being too narrow. It may eventually stretch to fit your foot, but your foot will be spilling out over the sides of the soles. Don't simply get a shoe that's half a size off because they don't have your actual size. You'll feel it in the morning. Ask the sales clerk to order you a pair in your size.
Once you have both shoes on, lace them up and see how they feel. There should be about 1/2-inch between your longest toe and the end of the shoe. You can tell by pushing down on the front of the shoe with your thumb to see what's air and what's toe. If you feel pain, you've hit toe. Walk around a bit or try running a few steps and jumping. The shoes should feel comfortable right away. Never mind what you may have heard about "breaking in" shoes; sneakers are designed for comfort, and if they're not working for you right off the bat, they're not the shoes for you. If there's room for your toe, your heel doesn't slip around and the shoes feel good, they are good candidates for your new pair. If they fit right, you'll know instantly.