Watch these two videos, Practice everyday or every other day, make sure your shot is after a exhale, thats when the body is most relaxed. Make sure your bow fits you and is not cranked down more than you should be. Some think its cool to shoot a bow maxed out. Not cool being overbowed. It will affect your shot groups, and you will get tired faster, when you could have been enjoying shooting more and getting more practice in with out tiring out too soon. Also, once you get tired, Stop for the day. Watch these two very good short videos, I promise, if you learn from this stuff I just wrote here , you will be a better shot. Also a great archer today told me I have to learn to play the wind. I moved my sights over to the left, now it is dead on target! we need to get some of that stuff in a little bottle to squeeze into the wind to tell us the direction of the wind.
http://www.bowtube.com/media/6/Get_A_Grip/
http://www.bowtube.com/media/32/The_Stance-_Wise_Shooting_Tips_With_Larry_Wise/