Watch for someone who avoids eye contact, they could be lying.
Someone who is lying probably won't use contractions.
People may use humor or sarcasm to avoid a question which avoids having to lie.
A person who turns away or avoids the person who is confronting them may be lying.
A person who is NOT lying will be more likely to lay a flat hand on their chest than someone who is.
A person might be lying if their emotions/expressions don't match what they are saying.