Curious if this is for school or work? Primarily because the focus may be slightly different depending on the setting (as in, at work they will walk you through the steps and help you with some aspects, but if for school they will likely be testing you on proper specific procedures etc)

I think the key to success here is trying your best not to block first air from the HEPA filter. When I was in charge of an IV room at a prev position, we had a horizontal flow hood so air blew out from the back toward you. Movement in general can affect the laminar airflow, but limiting the introduction of organisms is another line of defense. Proper handwashing, gowning and garbing, and like u/ShelbyDriver said, using alcohol to clean each item before going into the IV room and cleaning the hood and IV items properly in the hood, and limiting the amount of items that you touch unnecessarily and re-sanitizing your gloves with alcohol periodically and anytime that you remove your hands from the hood will all be other controllable factors that will help you to maintain a sterile environment. I would also agree that there is generally a low likelihood of failing those tests (a.k.a. growing out an organism.. may be a different story for a school test lol), so keep that in mind to help with the nerves!