Final answer:
The first thing a phlebotomist should do when performing an adult standard venipuncture is to apply a tourniquet.
Step-by-step explanation:
The first thing a phlebotomist should do when performing in adult standard venipuncture is to apply a tourniquet. A tourniquet is used to temporarily restrict blood flow and make the veins more visible and easier to access. By applying a tourniquet, the phlebotomist can locate a suitable vein for the venipuncture procedure. Once the appropriate vein is identified, the phlebotomist can proceed with the blood draw.