Experienced cookers put down a sheet of cardboard under the fryer so that oil doesn't stain the concrete.
Unlike what AKSWulfe said, do not DROP the turkey in, put it in slowly. A good way to avoid getting hit by splatter is to suspend the turkey hook from the center of a piece of wood and have two people lower it in. That way, you can be far from the turkey and lower it in slowly.
FULLY THAWED, and do NOT stuff it.
I've deep fried for the last 3-4 years, and am doing it again tomorrow. Tried a few injectors, no real benefit. Just do a bare turkey, and pat it down with a paper towel to get it as dry as possible.
One tip I didn't notice when I skimmed the topic, turn off the burner while you add the turkey. This helps prevent the risk of splashing oil from starting a fire. Get one of those long lighters to re-light it.
Stay away from overhangs! If something flares up, you don't want it burning down your house. Obviously, do not do this inside.
Finally, it's vital that you do this on level ground.