Spanish History Quizzes

Can you give me some tips to study for a test of Science / Bio?
I'ma pretty good student. I also worry a lot, and my friends they do not, most of them do not care about school though. I have an A in math, A in English, in the history of B, C in Spanish, and D and Science. I'm strong on some issues and some weak, as many. I do not know why, but no matter how much you study for science, just do not understand. I have read sections of this chapter and study the terms. But I always fail the tests and questionnaires. I always do my homework and take extra credit opportunity can get. But I started with a D and is now half of the semester and I'm still in a D. I need at least a C in science, so I can average my average 3.0 minimum.
Try talking to your teacher about it, I can help I do not understand and make sure you get a lot of sleep the night before test and eat a good breakfast. For the study, make cards yourself a study guide, flash and ask your friends to examine you. I hope this helped. Good luck:)