Observe Their Posture
When a person slouches while sitting down or standing up, it may indicate laziness. But this is not necessarily true, since he may have gotten used to that posture, but is not indeed lazy.
However, the most preferred posture is where one would keep his back straight with chin slightly up. This posture must be done without excessive tightening of the back muscles; otherwise he would look definitely stiff and awkward.
Obvious Signs Of Emotions
You can detect if a person is nervous if he finds it impossible to stay still. His body gestures would include fidgeting, tapping the hand or foot, drumming his fingers, pacing around the room back and forth, and trembling. Meanwhile frustration can be signified by a clenched fist, arms crossed over the chest, and the hands on the waist.
Confidence and comfort is reflected from one's good posture, maintenance of eye contact, relaxed use of hand gestures and body movements. The opposite of these gestures means otherwise – lack of confidence.
These signals from one's body language does not necessarily reflect what the person truly feels inside. His gestures may have been his mannerisms or simply actions that he has gotten used to. Thus, it is relevant as well not to be very judgmental in interpreting one's body language.