Wash your hair only every other day.
Make sure you're using a sulfate-free shampoo.
Use a scalp exfoliant once or twice a week, spaced out equally.
Make sure you're not deficient in anything (particularly Vitamin D3 and B vitamins) manage your stress, and don't think too much about it.
Beyond that, let your hair grow and treat it kindly, that's all.
Anything else is wasting money and time.