How can you prevent hammer toes?

Proper shoes/support: Well fitting supportive shoes with good biomechanical support will go along way. Some neurological, hereditaary or congenitial conditions may make this unavoidable.

Can't: You can try wearing proper shoes and stretching the toes.

Good fitting shoes: Avoid high heels. Have good genetics.

Comfortable shoes: There is a high genetic component to the condition. Avoid narrow tight shoes so that the toes are not subjected to prolonged periods of over contracture.

Possibly can't?: It all depends on the cause of the deformity. Some have a genetic component, some are created by muscle imbalance in your legs, and some can even be caused by nerve damage or disease. If you notice them forming, talk to your doctor about conservative procedures to straighten them before they get worse, if you're concerned.