This is not a foolproof method, but it is very effective for the most part.

1. Watch body language.
IF they are sweating or fidgeting it is a good sign of a lie.

2. Seek details.
ask person to repeat their story with greater detail. chances are they will mess up trying to come up with better detail

3. Be aware of unpleasantness
Low cooperation and negaitivity are often seen in liars

4. Observe eyecontct.
lack of eyecontact usually indicates lying

5. Look for signs of stress
look for small things like dialated pupils use of drugs or rise in vocal pitch

6. listen for pauses
if someone has to pause in the middle of a story then most likely they are having to make up as they go

7. Re ask questions
if you ask the same questions over and over they are likely to get their own details messed up as they go

8. be aware of too much protesting
if people complain too much or use phrases like
"to be honest" it is a sign they are lying