Before administering medication to a client the most important task you must perform to prevent germ transmission is

All care givers or healthcare workers must wash their hands, use gloves, and disinfect the area , if the medication is being given via the IV or IM method.

Explanation:

Hands carry germs . Washing hands will clean off most of the germs. It is important to wash your hands before giving medication so that you don't contaminate the medication or  the container that holds the medication.