A trick I used to use while in college was that if I ever dreaded the magnitude of the task that was in front of me (preparing for an exam, or working on my thesis or whatever), I'd spend half an hour making a very systematic time-table for it. So if it was preparing for an exam, I'd nicely spread all the chapters of the book I had to read into whatever time I had left. Even if the plan was a little unrealistic, the fact that I had made it made me feel in control of the situation and worked wonders for my mental state.