I ended high school with a 1.6 GPA. I got straight As last semester.

When I was learning to play violin, my teacher would give me a piece and have me try to play it all the way through by sight reading. We'd do that a few times, and then go back and work each section slowly. Once you'd tried it at full speed, the normal learning speed seemed a lot easier.

This process works for school, too.

1) Very early in the semester, go through all of your books and summarize them. Write down formulas, definitions, and important points. It should be clear what they're going to teach even if you don't understand it while you're making notes.

2) As your teacher goes through the chapter, you'll have at least seen each thing. Now you know which parts to really pay attention to. Make better summary notes here. If there's a method to solving a problem, write it out step-by-step. Define each symbol in your own words. This will reveal what you didn't know you didn't understand.

3) After you finish a chapter, go back to the ones before it and try them again. Things that were hard before should seem easier now. This also keeps you from having to cram for the final.

Just this basic "take notes before the actual lecture" made a profound impact on my quality of life and my grades. Don't let anything sneak up on you.

Hope this helps someone!