I was a decent student in University - I had a 3.8 GPA but that does not tell the whole story as my grades ranged from a C+ to an A+ as I was doing a Combined Computer Science and Mathematics major while also taking the pre-requisites for getting into medical school.
Even after going through university, I still did not know what I could have done to improve my experience if I went through it again (god forbid!). But I learned a few things from Cal Newport's book "How to become a straight-A student". He goes out to interview the straight A college students that are not just the ones that are grinding away all night to learn material. You probably know the students - these are the ones that do not have a social life, study all the time and just brute force learn the material and exams to get the best grades. In fact, Cal interviewed a lot of students who had very balanced lives and he wanted to learn from those students (he was also one of these students). Perhaps you're about to enter high school, you're already in college or you have to learn something (as a professional, you may have certifications or go back to school to do your MBA) - whatever the case, I know that there are a few tips here that will help you.
Schedule things in your calendar but be flexible
One of the most important things that a student can do is to plan out their day, noting down any events or appointments that are hard stops. Family dinners, social outings, sport practices, etc. Then out of those hard stops, figure out the blocks of time that you have in your day. For example, maybe you have 2 hours in the morning before your first class or you have a 1 hour block of time after class and before dinner. Use this time wisely because outputs is not just a function of the time you put in but about the work intensity (the more concentrated and focused you are, the more you can get done despite not having a lot of time). Also, consider the fact that as it gets to around bed time, you are going to lose focus and you are not going to be as effective - Cal notes that many of the students he interviews try to get a full night's rest rather than trying to push through the night and cram.
Be realistic about your work efforts
Okay, you have identified the blocks of time you have during your day. The next most important step is to be realistic about what you can get done (and not get done) during that time. The great thing about this approach is that you are working well ahead of any deadlines so you can start to work on assignments, studying, etc. in a piecemeal fashion where you slowly tackle and complete tasks.
Be flexible
Your schedule, set at the start of the day, is not set in stone. As things come up or as time frees up due to a cancelled class or social commitment, you can get more or less things done depending on what kind of time you have. Another example of being flexible: your dinner with friends has been moved forward an hour and now you instead of 2 hours to work on an assignment, you only have 1 hour. You can switch gears and work on another assignment that you may have in the pipeline (a shorter assignment).
Take smart notes
You may have heard about the cornell method or some other technique or method for taking notes. Cal's noted approach is not something that I have heard before: he says that a lot of students take notes using a "Question, Argument, Conclusion" structure - that is, to write down the question that the professor may be trying to answer, the steps that he takes to reach an answer and then the conclusion. When you take notes this way, it helps you evaluate the professor's lectures, fill in gaps with other materials and helps you to also write down sample questions that the professor may quiz you on during exams. In addition, most of your studying and critical thinking is through the note taking process which will save you time later when you go back to review your notes.
Study by testing yourself
The best way to study (and I unfortunately learned this in my later years of undergraduate) is to test yourself. Pretend that you are the professor and that you are quizzing your students about the material. List out the questions you would ask, then test yourself and test your knowledge to see if you can answer the questions without looking at your notes. If you have practice exams, supplement these questions with questions that you may have / come up with through your notes to develop a review package. Then go through the questions and test your knowledge, noting down those that gave you trouble. The next time you review, only go through the questions that you have noted and go through the same process until you can go through all the questions without any trouble. This then means that you are focusing your review on the questions / areas you do not know and that you are spending less time because you are not just reviewing all the materials over and over again - the amount of material you are reviewing is being reduced each time.
Yes, I'm not in university anymore but I am currently studying for my PMP and expect to do a few more certifications in the future. I won't have professors but I will certainly try to budget my time according to my schedule and what else I have going on, I'll be developing practice exams to test my knowledge and for review and I'll make sure that I take smart notes as I study. Cal, how come I didn't know about you back in university?