What causes low blood pressure and how can i make it higher?

Multiple things: Heart failure, adrenal insufficiency, unstable cardiac arrthymias (abnormal rhythms), sepsis with septic shock, neurogenic shock, cardiogenic shock, and most commonly dehydration. It depends how low it is, if low normal and you are not symptomatic you shouldn't get it higher. Smaller patients tend to have lower blood pressures as a whole.

Many causes: Low blood pressure is generally desirable, but if there is lightheadedness with position change or other symptoms of low blood pressure, need to ensure no underlying problems- low thyroid, or low cortisol, or slow heart rate. Need to ensure good hydration status, consider liberalizing salt intake. Compression stockings can be quite helpful. Some medications may include midodrine or florinef (fludrocortisone).