Find the perfect site, flat land is a must to ensure proper drainage and maximize the usefulness of your tent with proper placement.
Although I don't usually do more than a short walk-around to determine the tent location; I try to keep a number of things in mind.
I avoid known flash flood areas.
I normally try to put the tent on a gradual hump in the ground (rather than end up with it in a puddle/low place if it rains).
I try not to have it on a hill side that is so steep that I end up in a corner of the tent the next morning.
I try to put the tent into protected areas between trees and far enough from any road. to prevent it being run over if the area is invaded by partying drunk drivers during the night.
I try to avoid the tops of ridges where there is a likely hood of wind
I examine the trees around the potential campsite for lighting damage; it does tend to strike the same areas repeatedly, and I have had electronics burned out by near misses (near hits?).
...I avoid poison ivy patches...
I use a collapsible rake (or at least the side of my foot) to sweep aside small rocks, sticks and pine cones before I lay down the silver tarp that I use for a ground sheet... if there is a sharp root/stone sticking up, I move the tent to avoid it rather than have the floor punctured.
When entering a new area I try to scope out any standing/hanging dead wood; if there isn't any or the area is picked clean of potential firewood I look for an area that is not as over used.
I'm sure I have missed some things but that covers at least some of them...