Often underappreciated is the fact that your Personal Statement is your introduction to strangers. Interviewers have access to your Personal Statement prior to the interview. It should present a unified and genuine picture of you as a person, why you want to study medicine, and what personal experiences have driven your desire to pursue an MD. Grammar, spelling, and usage are important. You should consider asking trusted friends/family members/mentors to proofread your Personal Statement before submitting. Nonetheless, whatever you submit, you own. The bottom line to strive for is that the reader says after reading it: "Wow! I want to meet this person."
Remember that while extracurricular activities are important, they do not substitute for other credentials, especially good grades and MCAT scores. Our committee has expectations, and one of the biggest of them is that your decision to study medicine is founded on significant personal experiences, especially those involving meaningful patient contact.
If you interviewed, but didn't make it to the Waiting List, think: "I got the interview, so my grades, MCAT, Letters of Recommendation, and Personal Statement must have been at least okay. So, what does that leave?"
If you were on the Waiting List, but were not admitted, you should ask yourself the same question. Probably more discouraging is the answer to the first than to the second.
Either way, you might go to the library and check out a couple of books on evaluation interviews where you may find some interesting information about interview structure, purpose, and content.
A bonus tip for you if you are selected to interview: do your homework. Interviewers are generally impressed if you know something about the school you are visiting.