There are definitely many things you can do to make sure your college essay is the best it can be. One thing to consider when choosing a topic is to put forth something that is very unique to you. If you went through an unconventional experience, learned a lot from an extracurricular you do, or have an unconventional hobby, all these are very important. Keep in mind to use examples as you write as well. Don't just say that you like participating in your community -- back it up with examples of how you have done this.
Finally, make sure you leave yourself plenty of time to write the essay and proofread. One mistake I made in the admissions process was not letting anyone read my essays because I was shy about my writing. Having others, especially those you know well, review both the content as well as the writing helps you improve your essay and make sure that it highlights those things that really allow you to stand out as a candidate for admission.

One thing that really helped me was asking my English teacher to proofread it. If you have good relationships with your teachers, you should be able to get one to revise your essay. They can look to see if it would be good for college admissions and check your grammar at the same time!

Find a way to stand out! College admissions offices have to read hundreds of essays a day, so if you stand out, you're a shoo in!