It remains to find a trick to become extremely interested in your writing. One good way is to write from pain, to relate the subject in some way to your own pain.
I had a student who slept during class to mask his intimidation, but when he debated the Dream Act, which helps immigrants, he felt passionately about it. He was an immigrant. He argued well. He related to the subject.
You must think before you write. But think about what? Think about how it relates to your won pain (no matter how obliquely). Imagine yourself in the shoes of whoever is suffering in the case. Argue from his/her perspective.
Though not so easy, this tactic really does wonders for writing.