No one likes being lied to, but unfortunately, lies happen every day. There are ways to spot when people are lying, but it is important to remember that these steps will not work for every person.
Start by paying attention to a person. You cannot honestly know if a person is lying or not unless you know the person. Study their facial expressions and learn the way they normally act. Once you know the way a person normally acts, you will find it easier to detect their lies.
When the person talks to you, watch their eyes. Many times when people lie (not all the time, and not everyone) they tend to look off in one direction. For example, when someone lies, they may often look down and to the left. Other times, people will not make eye contact with you. They will look at their hands or pretend to be busy with something else. Pay attention to the eyes. They are like the window to our soul and you will be a better lie detector by studying someone's eyes.
Now look for other physical signs. They may fidget when they talk to you or something else out of the ordinary. Anything that they are doing a lot that they don't NORMALLY do when they are talking to you could indicate that they are lying. For example, when I have lied (come on, hasn't everyone?) I would bite my bottom lip and smile a bit. Yeah, I'm not too good at lying. So if you see me bite my lip and smile slightly, you can bet that I am most likely lying. This is why it is important to study the person you want to perform the lie detector test on. You need to know what is out of the ordinary for them.
Listen to their voice to detect lies. Many people tend to talk softer or LOUDER when they are lying. I once had a friend that would always speak louder than normal whenever she would lie. It was quite annoying and very obvious.
Listen for inconsistencies in their stories. People may not give any visible physical signs that they are lying, but they may not be very good at remembering all of their lies. If someone says they are going out for pizza at Domino's with Mark and Julie, and then the next day they talk about how they did something else, you can bet they were lying.
Most importantly, PAY ATTENTION to the person.
Obviously these signs will not work on everyone. Don't accuse anyone of lying without concrete proof.