Self-hypnosis involves the same ideas and techniques as hypnosis practiced by a trained hypnotherapist but individuals attempt to place themselves in a relaxed and hypnotic state. This is of course cheaper than paying a trained professional but can be difficult to master and may take a lot of practice.
One way self hypnosis is unintentionally and commonly practiced is whilst driving your car along a familiar route. Often whilst driving the mind will wander away from the task at hand. The feeling of reaching the destination without a real awareness of the journey is said to be similar to that of self hypnosis the relaxation of the conscious mind and the opening of the subconscious mind.
Through self-hypnosis it is thought that an individual can access their subconscious mind, convince it to believe they are a non-smoker and this belief will be carried over into the concious mind and concious behaviour. Hypnosis and self-hypnosis are also thought to help keep the individual in a calm state of mind which will in turn make dealing with the stresses of quiting smoking (and everyday life) easier to deal with.