The most effective job before going to college is to learn English, which is the most effective and helpful for you to take the postgraduate entrance examination and go abroad in the future. It is inefficient to study other mathematics or specialized courses, because the thinking mode of university is not the same as that of high school, so it will be more effective to study these courses when you adapt to the thinking mode of university. But English is different. I strongly suggest you go to New Oriental or learn it at home.