While for many people "just be yourself" is the only advice they need, personally I found a little preparation helped me to be much more relaxed and confident. I agree that "selling yourself" has a pretty sleazy connotation. But, rather than doing the "hard sell", think about it like this - the way to sell something is to believe in your product, educate the customer about why your product is the best, and then let them make a decision. If you think about it this way, it's actually pretty good advice for the interview.
In regards to the first point, if you don't believe in yourself, you won't come across as being genuine or having self confidence. Adcoms might wonder about your sincerity. As long as you were honest on your resume and PS, you should be able to talk with total confidence about the experiences and achievements that have brought you to this point. Sure, during an interview you can't honestly guarantee you'll ace med school, but you can demonstrate your belief that you definitely hold the the promise of a long, sucessful medical career.
The interview is also your opportunity to educate the customer - the adcoms- about your greatest strengths. What are your greatest strengths? If you're having trouble with this question, doing a short personal assessment can help to identify them. List all the jobs/schools you've attended. Identify your greatest accomplishments at each. Looking at the accomplishments, identify the skills or personality strengths that you demonstrated or gained. My advice is to pick three broad areas of skills to be your main points - for example, mine were academics, clinical experience, and leadership abilities. (I remembered this by ACL, like the ligament) So when asked that question "Tell me about yourself" I immediately started talking about ACL, giving specific examples of each. I could have used this question to talk about where I grew up or my family. Instead I used it to begin "selling myself". When other questions allowed ie "What are your strengths?" I once again emphasized my three basic skill areas. My responses were spontaneous enough not to sound canned, but they stayed on the message I wanted to communicate - "here are my strengths".
In regards to weaknesses, the key is to pick a weakness that under the right circumstances can be a strength. For example, if you are still reading this post, you might guess that one of my weaknesses is that I tend to over prepare (just a bit). While this lack of spontaneity is a weakness, over preparing for tests in med school is probably by far not the worst thing you could do. In contrast, a weakness like procrastination or shyness is pretty hard to paint in a favorable light.
Lastly, do some thinking about why you want to be a DO. I have met some people that have the most canned responses to this question - more holistic, spend more time with the patient, etc. Tell the story of how you discovered DO, or of the experience that led you to make the decision to pursue this career. For example, although I had heard of DOs, I didn't really know much about them until I found an old copy of "Foundations of Osteopathic Medicine" buried in the school library. Telling the story of pulling this dusty tome out of the library and discovering my future path has gotten a reaction from every adcom I've interviewed with.
Different strategies work for different people...based on my interviews this season, this strategy has definitely worked for me.
