If you're struggling in grades, you may have to adjust your studying habits (or lack, thereof).
Do homework w/out initially checking the back of the book for the answers.
Ask the teacher/professor questions. The only stupid question is the one that isn't asked.
Get in a (good) study group.
Practice, practice, practice.
Also depends on the class. W/c class is this for?
The first year of college, I would study in the University Union's Game Room to look at all the chicks. Not good. After a couple of Bs and some Cs, it was time to evaluate real quick.
Subsequent years, I would study in the University Library in three-hour blocks. Some can study in complete quiet. I studied with a cd-player playing anything from Classical to Old Skool to Jazz to Japanese Anime Soundtracks.
I would then break-off for a bite to eat, play a video game, talk to friends, log-in to the network. The break took about an hour, in w/c I would go back and the hit the books. For me, 3 hours was enough to lock-in on a week's course subject matter.
Your mileage may vary. After doing well on a midterm, reward yourself.
After kicking whup @$$ on a midterm, I would reward myself by purchasing a computer game or an anime tape (at the time). If I kicked whup @$$ on all my Finals during Finals Week (w/c I normally did thereafter), I would reward myself with a Computer upgrade, a couple of computer games, a couple of anime tapes, or a combination.
In the end, cramming is not the way to go. Some can get away w/it, some can't.
I knew someone who just purchased a TI-81 and was cramming on how to USE the ah heck and got very little done in studying for a Calculus midterm.