I generally give a short response because I tend to be busy. In this article, however, I will give all the answers I know. A good portion of intelligence is genetics. Some people are just born smarter. All this means is that they can concentrate better.
Intelligence is concentration.
Even if you concentrate well, there are probably things you can do to improve. The first step to concentration is clearing the body. There is a strong connection between body and mind. The best way to clear the body is vigorous exercise an hour of two before you intend to concentrate. During Regents week, I always ride my bike to school in order to accomplish this.