Considering my high school experience, I come to the conclusion that it has been one of the most interesting and fruitful periods of my life so far. If I were to give advice to perspective high school students, I would summarize all my ideas to three principles.
First and foremost, be socially active. Your high school life provides you with excellent opportunities for making new friends, socializing and making something useful, but truly enjoyable. Join the organization committee, school newspaper staff or even propose yourself for the President of your school. You will definitely have a lot of work to do apart from your studies, but this experience may be positive both in terms of your future admission to college and acquiring useful skills.
Second, however boring it sounds, pay attention to your studies. Although it may seem easy, you have a huge amount of work to do if you want to pass your exams successfully. So, it is much easier if you take your studies seriously and work slowly, but surely.
Finally, if you can, take up a sport or a hobby. Being a successful sportsman will increase your chances of getting a scholars as well as it may help in getting to know new people. Moreover, it will influence your health in a positive way, thus, increasing your quality of life.
So, if you want to recollect your high school years with pleasure, bear in mind the three key factors: socializing, studies ans sport. Moreover, remember that this period is one of the best ones in your life and try not to waste it in vain.