Based of the knowledge gained from "Left for Dead"(1 and 2), "Nazi Zombies", and many zombie movies, I have devised a plan that should work in the middle of any general situation.
Rule 1: Location
Always chose a location around or near food, water, ammo. Preferable a Wal-mart in the middle of an island where you own the gun shop and mistakenly obtained copious amounts of all ammo types... not all of us are very fortunate though in that aspect.
Rule 2: Scavenge
Everything can be useful, MacGyver it up out there and build a bomb out of spoons, forks, and CD's. Also grabbing extra food, ammo, water and wenches can't hurt you.
Rule 3: Weapons
All weapons can be useful, from gardening shears to an AA gun, it can be used. My recommendation is to have a variety of weapons and therefore ammo types. A 9mm handgun is a requirement, as well as a good hunting knife as well as a choice between assault rifle or sub-machine gun. My personal favorites are the ak47, C7, MP5, and Uzi. All of which brings me to my next point.
Rule 4: Zombie Anatomy
In worst case scenarios a head shot does not equal a kill therefore, be ready to run or blow off the zombies legs. A shot to the chest will not slow down a zombie; the dead do not need hearts or lungs, only stomachs. Disembowelment is always a good idea, mainly because if zombies do not have a stomach, how will they eat our brains?
In summary, always aim (ammo is scare enough as it is), if head shots don't work legs and disembowelment. Oh and a extra shot to a zombies head is more than worth it.
Rule 5: Company
Remember that this could be a very long drawn out fight between mankind and everything else, so choose teammates that could repopulate the earth and who can fight their way out of a encounter without you carrying them around everywhere.
Rule 6: Transportation
Now the last thing you want to do is to travel. You will be out in the open with absolutely no knowledge of the area, at least in comparison to that hidey-hole of yours. If the time arises, use horses. Sure you'll have to feed them, and they get tired, but they eat grass and if you really have to, you can harvest their dead body for food, and storage if playing Elder Scrolls IV: Oblivion. If horses become zombies and try to eat your brains, go to motorcycles or scooters, as long as they are slow. If they are fast, SUV, Hummer, armored trucks, etc. If fast and super-human strength, good job for surviving long enough and NEVER MOVE LOCATIONS.
Rule 7: Research
One can never know too much of ones enemy, when the time arises study, study, study. If it turns out that they can't swim, go in a boat. If they are afraid of dairy products, cling to cows. The best situations to research are when allies slowly turn or if you catch a lone sleeper, assuming they ever sleep. Remember, Nazi scientists did horrible things but made many great accomplishments. Ethics and morality leave when zombies strike, so dissect them alive and with little anesthetic.
When zombies do attack... well I'll just make another post to show my contingency plan.