Its a good idea to flip through some men's magazines and clothing catalogs to get some ideas for posing. Not only is practicing your facial expressions in the mirror very important, but so is practicing those expressions with different poses and body languages.
Now, I know the images below are of super skinny supermodels who have very long torsos... and to be honest with you, these ladies have been enhanced in Photoshop. Magazine images never go to print without retouching and enhancing, so don't be intimidated by them. We are using these images solely for the poses and body language. So try arching your back and resting your arm over your head as seen below, and then tweak the pose until it looks right with your body type. Practice your facial expressions while holding the poses.
Remember, everything in boudoir photography is exaggerated, so the poses aren't meant to be super comfortable lol. And if you are still struggling, don't worry, we will work with you about poses for your body type at your session. Its just good to have a little practice ahead of time. :)