The bedrock principle of neuro-linguistic programming (NLP) is that any action, behavior or emotion can be changed instantly as soon as a person's "State" can be changed.
Now here's the tricky part, what do NLP practitioners mean when they use the word, "State?" State is made up of two things, your physiology, which includes your posture, facial expression, movements, vocal tone, breathing, blood sugar level, and overall fitness and health condition.
The other element of State is called the person's "Internal Representation." Your Internal Representation is made up of how you perceive and what you believe about the things your senses signal to you. This means it can include your beliefs about yourself, your abilities, the type of person you are, and what you can or can not do. It can also include things like your belief system, like whether you believe the world is fair or is out to get you.
Now let's make this practical. Let's say you are usually very shy and have difficulty carrying on lively conversations with strangers. However, tonight you are planning to attend an important party and you want to improve your ability to engage in lively conversations, even though the room will be full of strangers.
There are two ways you can change your state in order to greatly improve your conversational style. The physiological way would be to walk into that room and act "as if" you were the most engaging person on the planet. You may stand in front of a mirror for a few minutes and straighten your post, hold your head erect and talk to the mirror "as if" you had a personality much like the President of the United States.
By doing this, by acting "as if" you were kind of person, your physiology, along with your breathing, posture and movements would immediately change your state, which would result in an immediate change in your behavior.
Now the second way to change your state is to change your "Internal Representation." You need to challenge and butly defeat the belief you have about yourself being shy and an awkward conversationalist. In fact, you need to turn that belief around so that you believe you are an excellent conversationalist.
You could do this by remembering a time you actually were in a situation in which you were engaging, friendly, outgoing, interesting and humorous. And guess what? That situation does not have to be just like the setting you are going into now. Perhaps the previous situation you recall, was when you were teaching a class full of children, but you "turned on" your personality so much that they loved every moment of their time with you.
You then bring the emotions of that previous situation and move them into a new representation you create for yourself. In other words, you use the emotions from another time and place and create a new internal representation to help you with this new setting.
NLP is a collection of wonderful tools, all designed to help you change your actions by changing your state.