Make time to study
By allowing yourself a few hours every night to study, at the same time every night, you will eventually make this a habit. Maybe you study best just before dinner, or maybe you prefer to study just before bed.
The key is consistency. Pick a time and stick to it. Soon, making time to study will become a habit.
Read your syllabus
In college, they hand out a syllabus at the beginning of each class to give you an overview of what will be expected. This should have tests, exams, quizzes, and midterms.
Use the syllabus as a guideline. If you know you have a test coming up, the syllabus can tell you (usually) how many points it will be worth. If you end up crunched for time and the quiz is only worth a few points, it may be better to spend your time studying for that biochem exam instead.
That does not mean neglect some courses in favor of others. It just means to know on the whole how much each test will be worth, so if you end up a little unprepared, you do not need to stress over it.