Hook up with the guys at Knox Off Road - there is usually someone going out a couple times a week. They also will organize "newbie" rides from time to time. If you ask to set up a newbie ride, someone will certainly want to go. (KnoxOffroad - Index page
Windrock is a cool place. Easy to extreme and everything in between.
Another "newbie" place that kinda fun is Nemo Tunnel. Abandoned trail tunnel you can drive through. Neat little area to explore.
Caryville flats (back side of Windrock) is nice and you get views like this -
The last trip I took up to the Flats was in October (we moved to Orlando in November). It was COLD up there but I just really love the scenery...