Your brain needs sleep so it can refresh itself, process all that information it took in that day, and gear up for the next day. If you don't sleep, your grades will suffer, you'll be in bad moods, and your body starts shutting down. Aim for a solid 8 or 9 hours a night. Sleep not only affects performance, but it also affects general understanding. The less sleep you have, the less your brain can even grasp the simplest of things. Aim for your first meal to be full of protein.  Breakfast provides the energy and nutrition for you to begin your day, be successful in the classroom and maintain proper development.  Protein and fiber-rich foods will provide you with the most energy. Stay away from empty breakfasts, like donuts and sugary cereals. Sure, you'll have an initial sugar rush, but that'll go away soon enough and you'll crash by 3rd period. And you'll be starving well before lunchtime! This may seem like a no-brainer, but many students are too afraid or don't care enough.  You're not dumb if you're asking for help – you are actually being smart.  Ask for help when it comes to homework, quizzes, and tests. If your teachers, parents, and tutors know you're trying your best, they'll want to help you through whatever it is you're facing. Ask for help when it comes to your general morale. High school is tough and it's easy to get stressed out. If your class load is hard to bear, talk to your teachers and counselor about it. They may have ideas to make it easier on you. You're only young once. College only gets more intense, so make sure you always leave time for a bit of fun. Set every Saturday night aside for friends, family, or just time to relax, kick back, and do whatever it is you feel like doing. If you don't, you'll burn out!  Fun is a necessary part of good grades. If you're miserable, not sleeping, and have no social life, there's no way you'll enjoy high school! Make time for fun so you can stay happy, focused, and do your best.

TL;DR in Indonesian:
Perbanyak tidur. Makanlah sarapan yang bagus setiap hari. Mintalah bantuan bila perlu. Luangkan waktu bersenang-senang.