I've always been told that sitting (like skeeter said above) is second-best to having a solid rest. Of course, you have to have some flexibility to get your elbow on the right part of your knee, and that's my problem with it because I have a tough time with flexibility period. My shot this year (my first year) was standing, with a sling (which helps stabilize one arm) and really pressing the gun into my shoulder hard (which helped to stabilize the other). It wasn't a long shot, though, and I doubt I would shoot over 200-250 yards standing like I was.

Nate