I've seen a lot of artwork in my time with a lot of poses of attractive women. In order to get really dynamic poses it really help to learn life drawing(which is something I am still learning.) People look at live posing models and get used to drawing things the way that they look in their natural habitats and how light, shadow, perspective, and foreshortening come into play. Once they become efficient at it, they can make artwork that looks like this.

However I've NEVER seen a real-life photograph of someone that captures the style that is used in some many pin-ups nowadays so perfectly. People usually have to take a 'normal' pose and then ad-lib to give it this look. Her pose, her expression, the lighting, the clothing choice, it's unreal. It's like a J. Scott Campbell character come to life!