First let me say HOORAH! You are doing a significant part of your work as a student by going to every class, taking notes in class, and doing the outside reading. I have talked to students who try to skip those steps, then complain about their grades. So pat yourself on the back, and keep it up! You are on the right track; you just need to do a little more.
In order to improve at this point, you need to analyze two things: the tests, and the way you are studying for the test. But remember--keep going to class; keep taking notes; keep doing the reading (though you may read my comments about strategies for reading to help you get more out of it).
You need to pore over any graded tests you've received. If your professor keeps the tests, then go during office hours and ask to look over the test in his or her presence. You have a right to look at your test.
Analyze the errors you made. Why did you make them?
Some errors are due to carelessness--you know that next time, you need to take your time, reread carefully, pay attention to clues. Sometimes, it's a matter of getting used to the way your professor words the questions (you might discuss the test questions--in a positive way-- with your professor to help gain insights on what he or she was thinking). That's another reason to study that test more.
Some errors are because you were familiar with key concepts, but did not understand them as well, nor did you memorize enough key facts in order to answer the question fully or correctly. Solution--make sure you study your notes in order to prepare for this situation. Create practice tests from your notes and from the book trying to copy the way your professor tested you.
Some errors are because you did not study the right material. For example, some students do not realize that a professor is going to be testing them from the book. Okay, fool me once, shame on you; fool me twice, shame on me. That can happen with the first test, but after that, you are warned, and you know what you need to do.
Some errors are because your notes were incomplete. If you need to improve in note taking, I encourage you to schedule a one-on-one appointment with a learning skills advisor or take a study skills class. But a quick fix you can try now is to find a study buddy (someone who is doing well in the class and who has legible notes) who will meet with you once a week or so to compare your notes. You can then fill in any gaps in your notes, and see an example of what good notes look like.
Some errors are because you ran out of time. Is that out of your control? In most cases, NO! If you are short on time during a test, it means you haven't studied enough so that you can find answers quickly. This problem occurs most often in problem-solving classes, and it means you did not practice the problems enough in your spare time. (Many students report that they do the homework one time, if that much. If you aren't able to finish your tests, then you haven't practiced enough problems). On concept tests, you haven't studied and memorized the concepts enough so that you immediately know the right answer.
So let's talk about how you are studying. If the *only* thing you've done is go to class, take notes, and read the textbook, that is not enough to do well on most college tests. (Okay, for some students it is, but that's just because life is not fair, and I'm not sure I can help you with that one. Although... I suspect that as you get more accomplished as a student and a reader, you might get more out of the time you spend in class, taking notes and reading textbooks, and then you may find yourself in a better position...)
Anyway, I'm going to tackle this one in a series of yes or no questions. The correct answer to all of these questions is YES, OF COURSE. If you answer no to some (or all of them), then consider trying these methods to improve in class.
If your answer is, Yes, Of course to all of these questions, and you are still having trouble, I recommend you make an appointment with a learning skills advisor. You also may need to consider dropping the class and considering other options such as: take a course that helps you learn skills needed to succeed. You may also benefit from discussing this situation with your academic advisor.
One final note: when you consider this list of tips, I want you to notice how different success in college is from success in high school. In high school, if you do what the teacher tells you to do, you usually succeed. In college, your professor may make some required assignments, but in general, it's up to you to create your own plan to study so you can do well on the test. You have many options--some of the strategies I mentioned may work for you; some may not. You are your own teacher in many respects, most particularly in deciding what you need to do for homework every day.
You can do it! Just get started.