My friend has low blood pressure, what can he do to fix this?

Salt & fluid: Give your friend a bag of potato chips, salted popcorn, or a can of salted peanuts and 16 oz of their (non-alcoholic) beverage of choice. That will raise the BP. He/she should be on a daily salt enhanced diet. There's so much about avoiding salt in our culture but salt is critical to our health and some people (like your friend) need to supplement it.