My inspiration vanishes when I'm feeling kind of low, or stressed about school, life, etc. So I think relaxing is a really good way to get back into it. To free your mind, write in a diary or journal. Write about what happened today, how you feel, where you're sitting and what its like there. Anything! And keep going till you've got it all out.
When I do this, I feel I start writing about problems I never knew I had, and it really reveals a lot about myself. After you do it, your head will feel clearer, and you'll feel happier. Its easier to be creative then. Also, read, read, read! And keep notes of what you like in that book or ideas you have. Or listen to your favorite music. It may get you hyped up.