I second Tiger Lily's suggestion of starting with an outline. After I do an outline, I write the body of the essay, then the conclusion, and then the introduction. I know that sounds a little backwards but I find the introduction to be the hardest part to write. If I insist on writing a perfect introduction before moving on, I would never finish the paper. I do know what points I want to make. It's just that the exact wording of the intro is hard to write.

The body of the essay is easier to write. I know what points I want to make, so I figure out how to make those points. The conclusion is generally just a short paragraph. The intro is harder because it has to capture the reader's interest and it sets the tone of the essay. When I first start writing the essay, I don't know what the tone will be. So I guess that's why intros are hard for me to write right off the bat.

Should inspiration hit, I write whatever section of the essay I'm inspired to write at the time. I don't have to write things in a particular order.

As Tiger Lily says, the essay doesn't have to be a work of art. It just has to be good enough to receiving a passing grade.