I have found body language and human lie detecting techniques very interesting, especially where they overlap. When people lie they tend to take defensive stances which include folding their arms in front of the torso or, if they are seated, leaning away from the person they are talking to. As far as facial cues go people often cover part of their face with their hand, in an attempt to hide other cues but this has become its own hint to lying. It is common to have heard that if someone is avoiding eye contact then they are lying, in fact any change in amount of eye contact can be a dead giveaway for lying. Keep in mind that in normal conversations people keep eye contact only 50% of the discussion.
If we look at body language alone to tell if someone is lying we will not be 100% accurate. There is no way to be 100% accurate with human lie detectors. Still, you cannot be anywhere close to being always right. You need to look at other reasons for the body language the accused liar is displaying. Defensive stances could also be caused by the person feeling uncomfortable with the person asking the questions, or they have been on edge due to outside influences.
Other signs of stressed body language are often linked to lying, because lying can bring up feelings of stress, you must think of what is causing the stress. Most lying body language is based on the person being stressed about having to deceive. When the person is stressed on their own it is mistaken for lies.
To help lower the anxiety of lying, and to lower any cues you may be unaware that you are giving, if you can believe in the lies yourself, you are more likely to be able to sell it. Confidence is sometimes enough to sell the lie, or to lower the suspicion enough so that the questioner will brush off any doubt.