1. Create a schedule for each week
With just a few weeks, assignments and exam preparation can become overwhelming. By creating a detailed weekly plan, you give yourself better chances at setting time aside not only for regular homework but studying and free time as well. By creating a plan and sticking to it, you are less likely to be stressed and more likely to be prepared for your exams.
2. Turn your phone off. Off-off.
Better yet, don't even bring your phone to your place of study. Try to get out of your room, go to the library or an empty classroom or somewhere else, and don't bring your phone. If you absolutely have to bring your phone, turn it all the way off. Not vibrate. Not silent. OFF. If you can help it, don't even bring a watch. Personally, I have found that it's easier to buckle down and "get in the zone" when I don't pay attention to the time. When you have no distractions or access to the outside world, it's easier to be focused.
3. Prioritize
Place classes that you are doing worse in at the top of your priority list so as to improve your grade to the best of your ability. Obviously if there is no hope left in the course, there is only so much you can do, but try to spend more time on assignments in those courses to help a little bit. Attempt to find a grade calculator to determine what you have to make on your final to get the grade you want in a course so you know how much time you need to devote to a particular course.
4. Start early
It is never too early to start preparing for finals. For me, finals is about 3 weeks way. Despite that it is Thanksgiving break, I started preparing for finals by trying to get ahead on the work I know that is due up until finals. I only have one course that requires a final paper and one that requires a final project, but I have started to prepare for my other finals by completing other basic assignments so that I have more time to focus on the big things later. The sooner you begin, the sooner you know what you do know, and, more importantly, what you don't.
5. Talk to professors
This connects directly to what you do and don't know. When you have an idea of what you may not know or what you need clarification on, you can ask professors for help. Not only will they be willing to help you (especially the earlier you ask), but they will probably be impressed that you asked before right before exams. Depending on your professor, you might be able to get an idea about what will be on the exam. Sometimes if you ask what to study for the exam, they will tell you what not to study so that you don't waste your time.