It's all about networking. Ask your buddies for their favorite trails. Find a group to go hiking with, take them somewhere new, and let them take you to new places.
But then again, there is something to be said about self discovery. Grab a map and start figuring it out. Look for rural type campgrounds (the lil red triangles) and hike out to them for a day hike if it's close. Theres also an option of going for a ride, and pulling off the road where you see a parking lot. Theres gotta be a reason for a parking lot in the middle of the forest. Usually theres a marked trail-head, but be careful. Take a compass, and always know which direction the road is. At the very least if the road runs N to S, and you head out walking E, you can always just walk W and eventually hit that road.
Of course the Self discovery option is assuming that you have a good head on your shoulders, and know a lil bit about taking care of yourself in the woods.