What can I do to prevent my toes from fracturing?

You can only try. There are no surefire ways of preventing broken toes other than to not break them! taking care of your bones is important- don't smoke, make sure you are getting adequate dietary calcium and vitamin d, deal with osteopenia or osteoporosis issues, wearing steel toe shoes at work if there is a risk of injury to the feet can help.
Avoid trauma. Try to avoid traumatic activities. Be cautious when walking. Clean up the house to avoid potential trauma and falls. Wear comfortable well fitting shoes. Make sure you have adequate calcium and vitamin d in you diet and do not smoke.