The more you can discuss leadership experiences the better.
You will have to do a good job of pulling the business implications from the technical aspects of your work. Many IT professionals only discuss the technical aspects in their essays and that doesn't go over well.
Make sure that you have some extracurricular / community service activities -- as you mentioned the competition is fierce, so you have to be able to stand out.
Make sure that you can discuss your career objectives in detail and why you want to pursue those objectives.
Similarly you have to do a good job of discussing why you want to attend a particular school and what you contribute while you are there and even perhaps after you graduate.