I've seen many models and I'll describe the worst , good, to best.
The worst model will do poses that are extreamly uncomfortable that cant be held for any real period of time, will pose then after stuttering decide a few mins into the pose that she wants to adjust, the artists then have to either erase everything or get a new sheet of paper or just redraw everything over again but darker. The end result is a forever shifting model. A pose that starts with the head pointed one way and ends in a completely different direction. If a pose cant be held for two mins, you are doing somthing wrong, most likly you arnt relaxed enough, or the pose is too hard.
A good model will get in comfortable poses. Understand that its not about being absolutly still, but about keeping your body comfortable enough so that it doesnt want to shift out of its position.
The best models, will be aware of thier eyeline, where their feet are pointed, and where thier hips and chest are pointed and will be able to get in and out the same pose by positioning those body parts in the same direction. The model will also study works of art and mimic those poses in a mirror and be able to get into that pose. The model will also know what poses are tough to keep and which are easy, reserving the hard poses for the 2-5mins warmups,, and the comfortable poses for the longer setups.
Keep in mind, you are the boss, you set the tone, dont be a premodana, but dont let anyone make you feel like you are a mannequin either. You want to be couteous of any artist's request, but you also dont want to be uncomfortable. Models will use thier breaks because the more comfortable they are, the better they can perform. Most models bring big tmers that can be used with feet. There are also books for models that will illustrate different poses.
The Nude Female Figure: 500 Classic Poses By Mark E. Smith is one I googled. Ive seen many around though.
I'll speak for all artists and say, Thank you, you provide a much apreciated service, and while some might be oblivious to how hard your job is, most of us do know that its a VERY difficult thing to do well.