For the most efficient management of their facial expressions, you must carefully examine your face. And each part separately. You clearly need to know what is happening with your eyebrows, lips, forehead on one point or another, with varying emotions. Once you have learned to take care of yourself, you need to start changing the reaction of each part of his face on the incoming information from the outside. Pay close attention to the movement of your face and try to prevent something that will reflect your negative state. For example, it is important to wean yourself wrinkle forehead or frown. Such things immediately give your mood and make the interlocutor draw their own conclusions about you, even if it is not true.
To the desired facial expressions have become natural to you, and did not look like willfully and wear a mask, as much as possible, practice in front of a mirror. Speak aloud to different emotional coloring phrases and see how this changes with your facial expressions. If it does not match what you say and how, start working on it this emotion.