Camping is simply the art of staying in one spot and picking off opponents.
Camping is the subject of constant bitching, but it does take a certain amount of cunning to do. If you wish to play an honourable game it is perhaps best to refrain from the technique a little. The most effective place to camp is at the quad damage above the level. It is rarely a good idea to camp at the rail, you are furthest from the action and it's easy to get knocked into the void. The quad camp is a little more effective, the only danger is an opponent coming up from behind.