In an article that came out in TBM in 2009, which coincidentally happened to be in a period during which I was attending many traditional archery clinics and making a concerted effort to improve my shooting, Dan Toelke was asked to list the three most common shooting problems he saw. Dan is better known for his bows than for his shooting instruction, but I know he has helped many traditional archers improve their shooting as well as provide some of the finest bows out there.
1. A sloppy or non-existent anchor. Use a tight, multi-point anchor.
2. Not getting the elbow back behind the arrow by applying back tension at full draw. Back tension can be an elusive concept for the beginning traditional archer, because we are not aware of that group of muscles in everyday life. But when you discover it, you will feel like you have suddenly taken 5-10 pounds off your bow weight.
3. Short drawing the bow, not opening up the bow limbs to utilize the bow's dynamic efficiency. This would seem to be the same as point #2, and there is some overlap, but it is possible to use back muscles and still short draw the bow, either by using a bow that was designed for a longer draw length, or by using poor alignment that results in a shorter draw length than your potential. See the permanent post at the top of this section, "Terry's form clock," for more information on this.
Dan concludes by saying that using a bow with too high a draw weight is a major contributing factor behind most of these problems.