In my many years of doing hypnosis I have learned that hypnosis can assist in focusing better than many other areas as it requires very little skill or motivation to improve your abilities to focus. When you are hypnotized you mind automatically begins to focus. That is the complete theory of hypnosis. Hypnosis is accomplished by teaching the person being hypnotized to focus. If the mind was to be compared to the body and you were to exercise every day, then your body would get stronger. If exercising to the mind was to be self-hypnosis and you did it every day and you focused each time you did it, then you would automatically begin to increase your ability to focus.
I taught a class at Wright College for many years and would tell my students to practice the self-hypnosis every day for one month. At the end of that month, their ability to focus would increase many times by just doing the self- hypnosis. Even by listening to a self-hypnosis CD, you can notice the ability to focus better by repetitive listening.