Liars often pull their body inward when lying to make themselves feel smaller and less noticeable. Many people will become squirmy and sometimes conceal their hands to subconsciously hide fidgety fingers. You might also observe shoulder shrugging.
Observe micro-facial expressions.
People will often give away a lie in their facial expression, but some of these facial expressions are subtle and difficult to spot. Some people will change their facial coloration to a slighter shade of pink, others will flare their nostrils slightly, bite their lip, perspire slightly, or blink rapidly. Each of these changes in facial expression signifies an increase in brain activity as lying begins.
Listen to tone, cadence, and sentence structures.
Often when a person is lying they will slightly change the tone and cadence of their speech. They might start speaking more quickly or slowly, and with either a higher or lower tone. Often, the sentences they use become more complex as their brain works on overdrive to keep up with their tale.