We are bringing in some of the posing tips which you should keep in mind while posing for a portrait.
OPEN THE MOUTH
Opening the mouth can set a different mood to the portrait. With the mouth closed the jawline clenches and adds extra weight to the sides of the face. It can also give a negative energy to the face.
Generally people have an instinct to lean backwards in a photo, when it happens we can see up their nose, into their mouth, and their eyes are partially closed. By bringing chin down we can avoid whatever is going on with the nose and mouth but we have to keep the eyes further open.
Unless you are professional model, most of the photographs of ours are in a fun mood. Well posing for the pics is good, but loosing up and being in a slightly light mood is always better.
BASIC UNDERSTANDING OF THE LIGHT
Consider you are posing with the arm up, now it can come up in the way of the light, this will make the arm brighter than the face and will also cast the shadow on the face. To avoid this just move the arm slightly backwards so its not in the way of the light.
Besides these, here are few video resources to help you out also.
POSES FOR BEGINNERS
SIX POSING TIPS FOR BEGINNERS