It really depends upon where you are geographically and how bad the bugs are.
I've camped where bugs are just pesky and I've camped (9-Mile Forest Service Campground in Northern MN in early June) where they were horrible.
In situations where bugs are really bad, DEET and a headnet are probably going to be the only thing that will work and only somewhat. Or maybe a combination of everything that people have mentioned here. A huge fan blowing couldn't hurt, but you'll have to confine yourself to sitting in front of it.
We tend to do most of our camping in later summer and fall and therefore avoid the worst bug seasons.