One of the hardest things about making a portrait is often the pose. Now I like to make as candid of portraits as possible, but not every client has the personality for such a shoot. Likewise, as a photographer it is not easy to memorize exactly a whole catalogue of poses, and even if you have done so, describing that in words to a client is not so easy.
This is why I really like the Posing App (available for iOS & Android). It is a visual way out in the field for me to show clients how to get into natural and attractive poses that will result in great portraits. The app breaks poses down by the number of people in a shot making it easy to find a collection of poses for the number of subjects. There is also a tips & tricks section. Just for how to better pose hands and arms the app is worth it.