You can learn to read facial expressions by becoming a keen observer of people. Notice how people react to certain situations and how their faces look when as they express different emotions. Studying both people you've known for years and strangers can help you become more aware of what facial expressions can reveal.
Facial expressions are a form of non-verbal communication just like other types of body language. Learning to read the face along with observing body language can really help you get an accurate reading. For instance, if a person crosses his or her arms and has the facial expression of darting eyes, discomfort and a guarded front is being communicated. You can then look for further clues as to what the emotional discomfort is or what the person seems to be hiding.
It's important to note that although indirect eye contact tends to mean that someone isn't being totally honest with you, too intense straight forward eyes can also be a sign of deceit. A person concerned about his or her facial expressions revealing too much could purposely try to keep direct eye contact. Look for forced effort rather than a natural way of maintaining eye contact. Sociopaths, who can be violent without experiencing guilt, are especially talented at maintaining the appearance of natural eye contact while actually concealing their true emotions. You may just simply feel somehow uncomfortable when in the presence of a sociopath because otherwise they can appear to be quite conventional and charming.
Reading facial expressions accurately is challenging, so practice is necessary. You shouldn't quickly judge an expression without giving it some analytical thought. Gut instinct is also an important consideration. It takes practice and the right mix of gut instinct and careful analysis to learn to read facial expressions well.
Some people's facial expressions may be subtle while others' are more animated. To make facial expression reading even more difficult, not all people react or communicate non-verbally in the same way. Slightly narrowed eyes for one person may signal suspicion, while for another person it may mean anger or annoyance. Raising the eyebrows up for most people means they're surprised.
Eyes tell the most when you're reading facial expressions, but other features can be telling as well. Pursing, or pulling in, the lips may mean that a person is trying not to reveal negative criticism. Wrinkling the nose may mean either disgust or confusion. Practicing daily to read faces can help you become increasingly accurate at it.