Hypnosis is the willingness to follow instructions during a heightened state of suggestibility. You can also think of it as a trance or state of focused concentration.
The main principle of hypnosis is to put the subjects into a suggestible state of mind and an implant the desired suggestions. In some cases, you do not want your subjects to be aware that they are being hypnotized.
For hypnosis to work best, you want your subject, to be relaxed and free of tension. Ideally you want them in a relaxed state of mind and a comfortable atmosphere.
If the subject knows they are being hypnotized, you can ask for their cooperation. Have them try to recognize any tension in their body and begin relaxing. Tell them to focus on places where they are tense and begin a mental effort to relax those areas.
When you are trying to secretly hypnotize someone, you can still try to reduce tension and get them relaxed. Avoid places where there are distractions such as loud noises or bright lights.
The secret to hypnosis is in getting someone to focus inwardly and enter a trance or state of suggestibility. Once they are in a trance, you can begin implanting suggestions.
You can find many courses and writings that talk about the real secrets to hypnosis. The website at hypnosis-x.info has some of the secret and controversial methods, though you may be able to find them by searching the web as well.