Look for micro-expressions. Micro-expressions are facial expressions that flash on a person's face for a fraction of a second and reveal the person's true emotion, underneath the lie. Some people may be naturally sensitive to them but almost anybody can train themselves to detect these micro-expressions.
Typically, in a person who is lying, his or her micro-expression will be an emotion of distress, characterized by the eyebrows being drawn upwards towards the middle of the forehead, causing short lines to appear across the skin of the forehead.
Look for nose touching and mouth covering. People tend to touch the nose more when lying and a great deal less when telling the truth. This is perhaps due to a rush of adrenaline to the capillaries in the nose, causing the nose to itch. A lying person is more likely to cover his or her mouth with a hand or to place the hands near the mouth, almost as if to cover the lies coming forth. If the mouth appears tense and the lips are pursed, this can indicate distress.
Check for sweating. People tend to sweat more when they lie. Actually, measuring sweat is one of the ways that the polygraph test (the "lie detector" in all the movies) determines a lie. Yet again, taken on its own, this is not always a reliable indication of lying. Some people may sweat a lot more just because of nervousness, shyness or a condition that causes the person to sweat more than normal. It's one indicator to be read along with a group of signs, such as trembling, blushing and difficulty in swallowing.
Watch out for fidgeting. A sign that someone is lying is that they fidget, either with their own body or with random things around them. Fidgeting results from nervous energy produced by a fear of being found out. In order to release the nervous energy, liars often fidget with a chair, a handkerchief, or a part of their body.
Watch the person's throat. A person may constantly be trying to lubricate their throat when they lie by swallowing, gulping or clearing their throat. Lying causes their body to increase production of adrenaline, which gets their saliva pumping and then creates very little. While the saliva is surging, the subject might be gulping it down. When the saliva is no longer surging, the subject might be clearing their throat.
Make your lie plausible. When you lie, only include information that is believable. Don’t exaggerate to a point where the listener will start to question what you are saying. Make your lie as realistic as possible.
Lie before you have to. You can avoid lying under pressure by initiating the conversation about the subject you are lying about. Lie voluntarily before you are asked anything. The listener may not think you are lying since you volunteered the information.
Be critical of your own lie and see if it seems reasonable. Don't use only your own judgment but think about if the person you are lying to will find it reasonable.
Practice saying the lie out loud. If something is true, it is often easier to remember, but if you are lying you may forget exactly what you want to say. Repeating a lie over and over again will help you deliver it more effectively.
Record a video of yourself lying. For small lies, the video camera is not necessary, but if you are preparing a big lie, video can help. Watch yourself on video to decide if the lie sounded convincing. If not, figure out a way to adjust it
Keep your hands away from your face. Liars tend to fidget with their hands a lot. Keep your hands at your sides if you are standing or on your lap if you are sitting. Don’t rub your chin or your nose. Don’t run your hands through your hair.
Control your blinking. Liars tend to blink nervously, and it’s an easy sign for people to notice. Also be aware that keeping your eyes open for too long can become suspicious, so make a conscious effort to blink as you normally would.