There's not enough time for this test! How can I maximize my score?
First off, try to pace yourself. There are 60 minutes for 50 multiple-choice questions: that's about 1 minute for each question, give or take. If you find yourself stuck on a problem, try to eliminate some of the choices if you can and move on: if you have time at the end, you can think more on the problems, but if you find yourself out of time, you have the option to randomly choose one of the remaining choices with more confidence (be aware that there are point deductions for incorrect answers). So instead of wasting time on hard problems, find and solve the easier problems to rack up your score: it doesn't feel good when time is called, and, while flipping through the test as you wait for your answer sheet to be collected, you find 10 questions at the end which you could've easily solved in like 4 minutes. Yikes. What's most important, though, is practice! Find problems from past tests and focus on your weak points, mimicking test conditions to accustom yourself to the time pressure. Constant practice will not only be great preparation for the test but will also help you keep calm and think more clearly during the real thing.
How do I improve my writing style?
Play around! Personally, reading a variety of books from different authors helped me develop my writing: for example, Patrick Ness showed me how large an impact a super short sentence can make. Also, although you should have proper grammar and know your grammar rules inside-out, don't be afraid to mess around with sentence structure a bit (I do it often for flow). Most importantly, good writing doesn't suddenly develop; you should keep writing, tweaking the way you write every now and then and seeing what you like best.
How can I make my college application stand out?
Show colleges that you're more than someone who only achieves high grades and test scores (though those are important too!). I think it's essential that you find extracurriculars that you really enjoy and can write about (passion is important) instead of ones that only look "good" on paper. Because a lot of schools require recommendations, you should definitely try to get to know your teachers more; that way, colleges will get a better feel for your personality and unique characteristics both in and outside the classroom. On essays, it's best to be genuine: find meaningful stories in your life that have changed you or your perspective somehow.