A good silica supplement,
Washing your hair less, like once a week (i'm assuming you have Caucasian hair - sorry if i'm wrong. Hair is not meant to be washed frequently. It starts a horrible cycle of stripping the natural oils in your hair and scalp, your scalp over-compensating by being overly oily, only to strip the oils away at your next shampoo. There are great shampoo-free resources on the internet),
Consider adding a natural oil of your hair and scalp regularly, at least once a week or the night before you wash your hair. Unrefined coconut oil is my fave,
And please, for the love of God, avoid any hair product with sodium laurel sulfate and also silicone (anything that ends with -"cone").