If they're fast zombies, YOU RUN. YOU RUN LIKE HELL AND NEVER STOP RUNNING.
If they're shambling zombies, you'll be okay, as long as you headshot them.
Speaking of which, headshots are the only way (allegedly) to kill a zombie.
Guns > Melee Weapons, ALWAYS, in a zombie apocalypse.
However, on the other hand, katanas don't run out of ammunition and are good at decapitating.
If a company called the Umbrella Corporation is ever created, everyone within range is to lynch the board of directors and whomever else is in charge immediately and burn their headquarters to the ground. Then nuke the headquarters from orbit just to be sure.
If the situation is desperate, try pretending to be a zombie until you can get to a safe hiding place.
Ignore the above suggestion if the zombies are controlled/possessed by malevolent spirits or Satan.
When all else fails, try joining the zombies. You may have to gnaw off your own hand as tribute and may need to take up cannibalism, but hey, you'll still be alive.