Colleges don’t want you to tell them things they already know. They know their campus is beautiful, their football team is top in their conference, and they have world class research facilities, in fact that information is contained on the homepage of their website! So you will need to dig a little. How can you do this? Google is an obvious choice, as is the school’s website. But, go beyond the homepage, read about your major and other unique programs. Be sure to check out the student life tab and get a feel for what it’s like to live there. Books like the Fiske Guide and Colleges that Change Lives can also give insight into a school. You can also try opinion websites such as Unigo, but beware, some opinion sites are really just rumor mills and should be taken with a grain of salt.
After you have gathered your information try writing down the qualities and programs that you like. If you don’t have any, are you sure you want to go there? You should only apply to colleges you want to attend. Even if the school you are writing for is your back-up school, I call it a “likely” school, if there is nothing there you want, you should probably look for another school.
After you have your list of programs and activities that genuinely interest you, then write something about yourself for each item that shows why you are good fit. Now you have some material to work with to show them why they the right for you and you are right for them. Try to add something about what you have to offer in additional to what they have to offer you. Even if the prompt doesn't specifically ask, inherent in “why us” is “why you.”
Your finished essay should make a convincing case to the admissions office that you and the college are a good fit. You don’t want to gush, and you need to be authentic—making stuff up just won’t pass the “smell test.” Finally, if you absolutely must add a line about the colors and the mascot, make sure you have the right ones! Many an admissions officer has read an essay with the cross town rival’s vital info inserted into a generic “why us” essay. That’s a college app don’t!