Being Not Attentive
Students tend to read exam instructions very fast without getting into details, thereby causing their low grades. Misinterpretation and rush will never make you get a good grade, so devote some time to reading/listening carefully. If you don't get something, you can always ask a professor.
The most known time killer for students is procrastination, but inappropriate time management is an issue that any typical college student follows. It is becoming increasingly difficult to ignore the fact that managing time wisely leads to better academic performance, so having a regular schedule, alarm clock, and making note-reminders can be enough for a good start.
Spending study time somewhere else is a great temptation, and some students make such college mistakes. If you skip a class, you still have to acquire this knowledge, and the professor won't listen to your childish excuses, except illness, of course.
Studying Too Hard
Studying too much won't make you a good learner, you need to have some rest and relaxation. Have an optimized schedule, which will keep you organized. If you want to work hard, you need to have a good rest, so do not try to cheat on your body and mind!
Too Many Parties
You won't argue, parties are cool, but you should balance your studying and having fun. Partying a lot may result in your psychological burnout, which is not good for your academic performance. So, use parties as the way of relaxing after a hard working week rather than a substitution for your academic activities.
Focusing On Private Life Too Much
College years is the time when students fall in love and start finding relationships with an opposite sex. It is quite natural, but falling in love should not lead to a complete insanity. Your beloved one won't leave you if you are at classes instead of holding his/her hand. Perhaps, he/she has to study, as well.