Remember that the way you approach studying and preparation for classes and tests are habits. If you have never really done any school work outside of the regular class time, then you may have to work very hard at developing new habits.
Too tired to do anything?
Sometimes you may feel overwhelmingly tired. So take care of yourself and take some time out. You will notice an adjustment period , especially at the beginning of the semester, during which you will require more sleep. It is not uncommon to sleep 12 hours straight until you are back into the rhythm of heavy brainwork.
However, if you generally can't get yourself started on your assignments and homework, then you may have an overall motivational problem. During the demanding times, it is the end goal, e.g. your chosen career, that will keep you motivated to put forth the required effort. If that end goal is not clear, then it is hard to exert the effort. The key element here is that the end goal has to be your goal -- not your parents' or what you think others might expect from you. You have to want it. Career exploration with a counselor can be an excellent way to help you discover what you want.
The Nature of Change
Theories on the nature of change have shown that change is accomplished through different stages and may not be as easy as it seems, often requiring outside help. Take small steps; set short-term achievable goals, and reward yourself when you accomplish these goals.
Overcoming Procrastination: Manage your time. Get it all Done - This article discusses some common causes to procrastination and tips for dealing with them.
Elements of Motivation - This site offers excellent links to the following aspects of motivation: Three elements of motivation, Visions and lifestyles, 7 rules of motivation, Develop a dream, Perseverance, Overcoming failure, Comfort zones, and A goal is a journey of decisions.