Step 1. Fluid resuscitation.
It depends. If you mean low blood pressure in a seriously ill, hospitalized person (i.e. Septic shock) then generally we give fluids and sometimes certain medications to support the blood pressure, and we try to treat the underlying cause. If you mean a low-ish blood pressure in say a healthy person with no symptoms or signs of ill-effect, then often we don't do anything. In between? Probably further eval.
More info please. What are you defining as low BP? While goal BP is.