Finding good campsites is a necessity for ultralight camping. It is one example of using your head instead of your (heavy pack carrying) back because a good campsite can extend the range of your gear. For example, it may be 28 in the valley, but above freezing up the slope.
Assuming you have choices and are not locked into camping in designated areas (or assuming you go ahead and stealth camp):
1) Identify micro-environments that are more likely to be comfortable. Half-way up a slope is warmer in the cold and cooler in the heat than either the ridge top or the valley floor. Valleys are frost pockets and ridges have wind. But in hot weather, valleys are more humid and closed (and mosquito ridden) while ridges are less likely to have cooling convective breezes. (But there are exceptions.) Be aware of the prevailing winds and the directions of storm movement in the season during which you are packing, and locate your camp accordingly. That ridge top with a cooling breeze may turn into a hell of high winds, lashing rain and lightning within a few hours.
2) The terraine in forest environments is generally highly variable. Almost every slope will have its benches, and large trees can make flat places where they fall over and turn up a root ball or just upslope of a large log. However, it may take some close looking and bushwhacking to locate a good site. Don't get disoriented or lost.
3) One advantage of hammocks is you can hang them over any ground - increasing your choice of campsites astronomically. But be careful. If a rope or a knot fails, a few inches in height can make the difference between embarrassment and serious injury. On a slope, ALWAYS put your head uphill and close to the ground. That way, if something fails, you are less likely to break your neck or to fall far or to roll. Always keep the hammock as low as possible without hitting the ground.
4) To locate a good campsite without being able to see through the woods, look at the terraine. A topo map may or may not help, but if you can read it, look for wide separation between the contour lines which indicates flatter ground. As you hike, pay attention to the general behavior of the terraine. In glatial areas, the valley's are U shaped with steep slopes near the ridge tops. In areas of water erosion, valleys are V shaped with gradually increasing slope from the ridge tops - unless there is cap rock. There may be benches like steps up the valley wall, depending on the geological history of the area. Got that? No? I didn't think so. Just pay attention. You'll start to see where the good sites are likely to be wherever you hike. Don't forget to watch for stealthy trails that head off into the woods. Unless they are just game trails, they may indicate where old hands in the area have their usual campsites.
5) One of the frustrations of the AT is that the southern half runs narrow ridges with few good off-trail sites what are out of sight - unless you go way down the ridge. That makes finding micro-sites like root balls and logs more important.
6) On the AT, many folks start off camping away from the shelters and established sites, but end up relying on them instead of taking the time to find a good stealth site at the end of the day when they are whupped. Also, the only water is usually near the established sites. That increases the pressure to use them. Again, hammocks avoid the problems of rock-hard, eroded, dished out and puddled tent sites.