Whether you are a normal person, or an authority figure, you need to know if someone is lying, because you won't always have a Polygraph
Step 1: If They Change Their Tone/Attitude
If a person is mad, then calms down, or calms down and gets mad, they're lying
Step 2: If Someone "swears"
For example someone says "I swear to God that I didn't break the cup", they have some chance of lying. Truthful people don't this far, and I know from experience.
Step 3: Too Specific
The liar will not know how to tell a great lie so they will make it into a complicated story. For example "I got an F on my report card because on Monday at 2 o clock, it was testing and I didn't get enough time"
Step 4: If They Avoid Eye Contact
If they don't look you in the eye, they are probably lying because they don't want to be noticed so this means that they don't want the person to know the truth.
Step 5: Moving Fingers/Toes
A truthful person doesn't move toes and fingers. Liars do this because they are scared and nervous that someone will know the truth.