Teachers love it when students who get a bad grade show a willingness to learn and get better. That makes the teacher feel successful, like they're doing a good job. So if you go up to a teacher after a bad grade and say something like "Hi Ms. Kowalski, I'm not happy with my performance on the test. Could we go over the problems that I missed or talk about preparing better in the future," they just might faint with satisfaction. Even though it's really hard to do, a lot of good can come from meeting with your teacher:  The teacher will explain problems you missed or ideas you struggle with The teacher will see that you want to learn and may factor this into your final grade The teacher may give you extra credit work It feels good to help other people, which is why many students who ace tests offer to help out students who didn't. Just be sure to actually spend time studying and working on improving instead of goofing off. And remember to try to choose someone you're not attracted to or have a secret crush on — we all know how much "studying" gets done when you're in the same room as a total man-hunk or she-angel. Although you may not have to tell your parents, it may very well be a good idea. Your parents care about you succeeding. That's why they show concern over a bad grade — not because they want you to feel bad. Remembering this will help you open up and hopefully make getting help a lot easier. Your parents may sit down and explain to you what you got wrong; they may hire a private instructor or tutor to help you out; they may schedule a meeting with your teacher (even though this is unusual after just one bad grade) in order to learn how you could improve.

TL;DR in Chinese:
找你的任课老师讨论改进的方法，如果学生虽然有一次成绩不理想，但是仍表现出了强烈的学习和向上的意志，老师就会很喜欢这样的学生，这会让老师感到成功的快感，使他们觉得自己做得不错。 向那些考得好的学生寻求帮助。 考虑告诉父母你这次成绩不理想。