When you first arrive at a potential campsite, take a look around. Where is it in proximity to water and to the trail? While you should never camp less than 200 feet (61 meters) from a water source, you should at least be close enough to one for dishwashing, cooking and bathing purposes. A campsite should also be at least 200 feet (61 meters) from the trail; that way both you and the people hiking on the trail enjoy greater solitude. Also, pick a spot that's flat. If you can't find a perfectly level location, be sure to orient your tent so that your head will be higher than your feet. Before you put up your tent, clear any rocks, sticks and pinecones that might poke you in the back while you're trying to snooze.
Think about the weather conditions. If it's hot, camp in a shady forest where the sun is less intense. If it's cool, orient your tent to the east so that the warm rays of the morning sun wake you. Avoid narrow valleys, ridge tops, and notches or low points in a ridge where strong winds develop. If it's windy pretty much everywhere, try camping behind a windbreak like a bush or boulder. And whether it's windy or not, survey the immediate area for dead trees or broken limbs known as widowmakers that could potentially crash into your tent during the night.
Rain has the potential to cause problems as well. If you camp in a low spot, it may collect water during a storm, or worse, that water could wash you away during a flash flood. Higher ground tends to drain better, and as a bonus, it'll stay warmer at night since cooler air tends to sink into depressed areas. Finally, consider how well your campsite is protected from lightning if storms are threatening. Avoid high points, exposed areas and taller trees in favor of areas partway down a slope that aren't likely to flood.