hrmk

I am not sure if it is appropriate to write here though, I have a problem about a writing sample. I am not a native English speaker and applied MA. Since I have been asked from the university to submit a 3000 words writing sample for their final decision as soon as possible, I got nervous. I have not written such a long essay in English. Does anybody know how to make a structure to write such a long essay?? I am happy if anybody tell me.