1. Keep all skeletons in the closet.
Have any embarrassing photos and videos online? A criminal record? A bad history? College applications are not the time to bring them up. Although college is often regarded as the time to throw away the past and "reinvent" yourself, you have to be accepted first.
Avoid the "I was lost, and now I'm found" confession, and don't try the "I have a complicated past" essay prompt unless you can really pull it off. College admission officers don't want to read about highly vivid descriptions of illegal substances.
2. Dress to impress.
Don't show up for school tours wearing paraphernalia of another school, or putting on the sweater you just bought at the campus bookstore before the tour. Not only do you want to appear suave and professional, but you also you don't want to look eager and desperate -- and nothing is more embarrassing than Dad carrying around foam fingers and screaming the school's football song every ten minutes on the tour.
If you have an interview session planned, be sure to wear something that's casual, yet not too informal. Any button-up with nice shorts or slacks will do. Make sure you pop in a breath mint (and finish it) before the interview to get rid of the onion bagel breath.
3. Don't kiss your interviewer.
Making the wrong impression on your interviewer can often have damaging efforts, more so on your conscience than your admissions status. Try to keep a professional, yet casual approach.
Keep all of your mannerisms in check ("pleases" and "thank you's" can go a long way). When it comes time to meet them, look them directly in the eye, smile, and have a firm handshake. If possible, open doors for them or others. Other good practices: sitting (not slouching) in your chair and putting your smartphone away (it's only for about 30 minutes).
Come prepared with questions about the school, preferably ones you can't find on the website, because, otherwise, you'll just look lazy (i.e. what is the student culture like? how often do students meet with their professors outside of the classroom?).
4. Don't pretend to be somebody you're not.
Didn't write a best-seller? Not the MVP on your sports team? Not Dan Humphrey? Don't pretend to be.
Nothing is worse than getting caught up in a white lie, especially on your college application journey. Most of the time, the same change you make won't make that huge of a difference, because, let's face it: Everyone is in National Honors Society, most people have enough volunteer hours to earn them a shiny medal, and one extra position as secretary of your school's nonexistent environmentalist fashion student club won't help unless you actually founded your school's first environmentalist fashion club.
5. Instead, be honest. Humble, yet honest.
Worked your butt off during high school (or didn't)? Be honest about it. There's no need to embellish something that wasn't entirely your favorite activity, or masquerade about something you liked but might seem weird.
Personal anecdote: My personal essays for college applications included very obscene topics, one of them being the intersection of art and sex with culture in South America. Why the hell did I write something like that? Because it interested me. And, by the looks of it, it interested my admission officers.
So, again, be honest. It's a lot easier (and more efficient) than putting on a facade of someone you're not.
6. And the pettiness known as high school competition?
Leave it at home.
There's no need to be competing against your classmates for an acceptance letter; there's so much more competition outside your hometown.
For more tips and horrible pop culture references, check out the revised College Advice blog, freshly stocked with biased college reviews and honest answers to all of your college admission needs.