I know, I know — "drink more water" seems to be the solution for everything. But in this case, I really believe it's true. Dehydration has a number of side effects, including fatigue.
I've found that this healthy habit actually starts the night before. I try to drink a glass of water before I go to sleep and then again first thing in the morning. This immediately helps me feel more awake and less likely to succumb to the daunting desire to hit snooze.