There are numerous places to go for assistance on writing a college application essay. Dozens of websites, publications, and books are devoted to helping students with their essays. There is no one simple equation for an effective essay, but, like the student writing them, each is unique.
Often, these books, publications, and websites do publish examples of college application essays. Reading other essays is a great way to get a sense of the broad variety of writing out there. You should read what others have written. Use these essays to stimulate your own imagination for what you want to write. Remember, each essay should be deeply personal and original. There's nothing wrong with getting ideas from what others write, but your essay should be a reflection of you, and only you.
To help you get a better sense of what colleges are looking for, here is a couple of pages from a Newsweek publication about what makes an essay good. Not every page is available free online, but pages 3 to 6 contain some helpful information.
Another resource is the book 100 Successful College Application Essays and there are some good excerpts published here.
Last year, a Colorado high school set up a group page for all its seniors to post and share their college essays. The purpose was to encourage collaboration and peer-to-peer feedback. It's an interesting idea and you can see all their essays here. Not all may be final drafts, but you can read what other high school students are writing about.
The publication Teen Ink also carries numerous college application essays. They publish a monthly literary magazine aimed at high school writing classes. Their website has a section of popular application essays. Their site also contains other, helpful information about colleges, all written by teens.
Hope these resources help you as you begin writing your essay. Remember, we need a workable draft for class on Thursday. Good luck.