I asked Stacy Nelson, a no less than stellar instructor with the Appleseed Project, what he thought the primary error or most common mistake women make, in his experience. He have me a fantastic answer:

“My experience is not that women are more timid.  Actually, the women I have taught on the line have really been quite assertive and great students.   Better than men in general.   Some of the toughest aspects of teaching women is that they often lack the gun culture exposure, thus the need to break the shooting process down to a more fundamental level.   They lack the “firearm vocabulary” and often come to us as a clean slate.
This is also one reason women make better students.   They learn what they are taught, they don’t have to first unlearn what they thought they knew.   We very often see women shoot better, improve more, in the two day course than men.   I attribute this to women not having to struggle with previously learned mistakes or improper techniques, they simple listen, learn and apply.
We have had many women state that they were intimidated to come to the shoots, for many of the reasons mentioned above, but thankfully, they are put to ease rather quickly.   Frankly, we may experience more “timidness” from the men, but they manifest it in either not showing up or in being hard headed in receiving instruction.
The biggest mistakes I have seen are simply body coordination issues.   Women often approach the techniques of handling a rifle, initially, in an awkward fashion.   Part of this is lack of familiarity, part is because their body is built differently.   The lessor upper body strength, higher center of gravity and smaller shoulders are just some of the aspects which need to be worked around and into the different positions we shoot from.   Not impediments, just a little different.”
Nice… Thanks Stacy!