Live and learn - and it's good you realize you need to practice. My advice, which seems to have made my hunting shots a LOT better - practice in the contorted positions and funky rests you will be using in the woods. It looks funny at the range since 99% of the guys out there are just sitting at the bench doing their careful shooting. But I always do all my shooting in wierd positions after I get sighted in. At that point I'm also practicing quick but accurate second shot - and accuracy is measured not by the 1 inch bullseye, but the 8 inch kill-zone circle. (which I improve upon the more I practice, but I never am bummed if I can hit that circle from my awkward positions).

And when you're in position for hunting, rehearse positions, movments, rests, etc. I can't tell you how many chickadees and squirrels I've drawn down on - it relieves boredom and I think if done realistically (quietly, slowly, etc). it doesn't spook deer.