Do you want to do well in school, or do you want to do good (as in good deeds) while you are at school? Learning the difference might help your grade in English class.
With all the resources freely available these days, I see no reason why anyone with internet access shouldn't be receiving excellent grades. I think the problem is this generation is using the internet too often for entertainment instead of education.
One place you might want to check out is Khan Academy. It's an online tutorial site with short quizzes to make sure you are learning the material. There are many different subjects offered, and if you have a Google account (such as Gmail) you can track your progress.
I looked around for studying tips and ways to get all A's. DEFFINATLEY make sure to ask your smart or determined friends what they do to keep their GPA high. Advice from piers is 100x better then online resources (In my opinion!)
Most of all, don't stress it! That's school time stuff worry about it a little closer to the school year,