There are two keys to posing. First is to "break symmetry." The second is to keep "in the light."
A person standing with arms at their sides looking right into the camera looks posed and "boring." However, look through the fashion magazines and not how the model's body is often twisted, with the hips pointing a different direction than the chest, and the face may be pointing yet an entirely different direction. Also look at the hands and feet. Notice how one hand is higher than the other and that the feet are often pointed different directions or standing on different "levels?"

It is this "broken symmetry" which makes photos look interesting and dynamic. It looks like the model is actually moving and doing something even though they may be perfectly still in the pose.

The other main rule is to "find your light." The photographer will normally have one light which is far brighter than the others. For the most part -- you want to point your chest and face toward that light -- so that the important parts of your body are lit well. Of course the photographer may tell you to point your body different ways -- but this is to emphasize different parts of the body. However if the photographer isn't giving you much for directions -- try to keep pointed "toward the light.

How you pose will depend upon the way that the photographer likes to work. Some photographers prefer models who "move to the music" and simply takes "snapshots" when he/she sees something they like. Other photographer's will meticulously pose every little detail -- down to what direction your fingernails are pointing. With the first type of photographer -- the best thing is to "KEEP MOVING." With the second type of photographer -- the best thing is to "NOT MOVE AT ALL." You will have to learn to adapt to the style of the photographer you are working with -- and he/she may have to adapt to you somewhat as well.

It's best to work with some really good and experienced photographers when you are just starting out. They will teach you some tricks and some methods which will help you look your best -- even if you are working with more amateur photographers in the future. If you start out working with amateur photographers who don't know what they are doing (or how to instruct you how to pose to make you look good) then you are just wasting your time. If on the other hand, you've learned some basic posing techniques -- then your time spent with ANY photographer will be more productive.