Any underlying anxieties or other types of psychological stress will affect your sleep - exam stress, job stress, work deadlines, relationships, financial stress, etc.
Likewise anything that excites will also affect sleep - excitement about new work ideas, imminent promotion, graduation, marriage, etc.
Some tips that've worked for me -
-Stress management - staying organized, exercising, breath control, long walks, focusing the mind, etc.
-"Clear" the mind - meditate, breath control and "watch" the breath go in & out. I use to laugh at this concept, but it magically helped me.
-Stick to a sleep routine - drop dead in bed by ....pm and arise at ....am. Do it for a few days and it automatically sets into your body.
-If you are a light sleeper, then make sure your room is absolutely dark. You don't want the eye and skin sending messages to your brain about the presence of light. This will affect your sleep.
Most of all, best of luck for the exams. You will do very well!