well, so far Im pretty new to this, and I go to about every cache twice. 1st time I go to scout the area. I look around, try to figure out where Im going to, exactly where Im going to. Typically I will glance around a bit to see if I can score a quick find, but if I cant thats ok. I then usually go back either later in the day, or a day or two later, to actually give a good going over the area.
In trying not to draw to much attention (especially in high muggle areas), I find this makes it easier to get in and out with out hanging around for a long time. I dont personally consider this a DNF, maybe it is to some. When I look high and low, to a point where Im completely stuck and still cant find it, THEN I will post a DNF.