You can learn to write. You need to make sure that you understand the prompt, and that you know how it is graded. Make sure that you plan your writing, so that you're not just drifting in any old direction. Write with purpose. Make sure that what you wrote answers the prompt, when you are done. Also, make absolutely certain not to use any words that you are not sure you are using correctly. That includes being unsure how to spell them. Once upon a time, people became great writers by reading a lot of literature written by other great writers. That's a strategy for the long haul. In the short term, for this test, you will need to read all of the study information on the website. As you have been told, practice writing from a prompt every single day. See if you can get a friend to read and critique your writing. If you're friend is an English major, so much the better! If you don't know someone, this is worth hiring a tutor for. Grad school is all about writing.