Watch their eye movement - The eyes of dishonest people will tend to move around a lot to avoid meeting your gaze. However, staring at your eyes for prolonged periods is also an indicator of a lie.
Are they defensive? Guilty people usually get defensive at the first indication of an accusation whereas honest people will get offensive.
How is their stance? - Liars often feel uncomfortable standing directly in front of an accuser and may avoid standing with their shoulders squared to yours. Instead, they might stand slightly to the side or with their shoulders offset.
Look at their expressions - Expressions are limited to the mouth, e.g. if a liar fakes a smile, he will only use selected muscles whereas a natural smile utilizes muscles over the whole face.
Are they playing with something? Liars will play with objects in their possession such as a handbag, bracelet, mobile phone or hair. They may also put an obstruction between themselves and the other person, often something as simple as a coffee cup. This is a subconscious way of attempting to ‘barricade' themselves to relieve the tension of lying.
Watch that tone - A liar's tone of voice is often not consistent with his/her gestures or statements.
What are they saying? Dishonest people will often use sarcasm when answering accusations.
Did they answer your question? - A liar uses your words to answer questions, e.g. Q: "Did you have sexual relations with this woman?" A: "I did not have sexual relations with that woman."
Check out the details - Dishonest people will add unnecessary detail to the conversation; this is an attempt to comfort the other person.
Did it make sense? Often liars' words won't make sense and their grammar may be incorrect. This is because a liar's mind is racing in search of a convincing answer and the signals to the mouth are sent incorrectly.