You can use heat to soften the material of your new shoes. Using a blow dryer, blast your shoes with air (make sure to move the blow dryer around to evenly distribute the air and avoid melting the material). Once the material is warmed up and more pliable, gently twist and bend the shoes in the center to break them in. Don't go overboard and bend them so far that they don't return to their natural shape, or so hard that they break.
Keep silica gel packets in your shoes when they’re not being worn. Have you noticed after purchasing a pair of new shoes those little white packets containing tiny clear balls inside your shoe box? Those packets contain silica gel which absorb moisture and keep your shoes from shrinking. Hold on to those packets instead of throwing them away and stick them in your shoes when you’re not wearing them. You can ask a shoe store associate for extras, if necessary.