Acute or chronic? Acute, severe hypotension usually involves a critical illness, e.g. Overwhelming bacterial infection, massive heart attack, etc and requires treatment of underlying cause in icu, often IV fluids to support the circulation, and sometimes strong meds to constrict arteries and raise the pressure. Chronic low BP usually requires oral hydration, esp with electrolytes (e.g. Gatorade or coconut water).
Depends on cause. I advise people with low blood pressure and symptoms to consume salty foods, because the higher sodium content can bring up the pressure. U should drink 2 liters/day. In rare instances, I use Fludrocortisone to increase bp. In really tough cases, I use midodrine. These are both prescription meds. I have seen people use theophylline for this, or you could try good old fashioned coffee.