Before writing, do as much research as you can. You want to be able to show that you understand how you are going to take advantage of the resources and opportunities available at Columbia Business School. Find out what is important to the university and then show how what you have to offer matches those things.
Once you have done your research, take the time to plan out your essay. Doing so will help to keep you on track and take full advantage of the word limit. After writing your essay, make sure that it is free of grammatical errors and typos.
Though it may sound trivial, editing and proofreading your essay is another way that you can improve the strength of your writing. Reading your essay out loud is a great way to evaluate the quality of your writing.
The places that sound awkward are the areas that you should revise. Having someone you trust to look over your essay is also a good idea before you submit it. A second pair of eyes will provide you with a fresh perspective and can help you determine whether or not your points are coming across the way you want them to in your essay.