Employ dynamic rest. Cease the offending activity. For how long varies depending on the severity of your injury, but expect at least a month. You can cross-train with swimming and biking as long as you don’t load the injury.
Support your arches. Orthotics (arch supports) can help fix pronation and improve your running mechanics. Over-the-counter products usually work just fine, but if not, consider custom orthotics.
Supplement. Eat more calcium- and vitamin D-rich foods or take supplements.