What can I do to make my application stand out?
This really isn't any different for DOs than any other applicant. Work hard, get good grades, glowing LORs, write a great personal statement, and interview with a smile. You may choose to address briefly your choice to go to Osteopathic school in your personal statement, or how you believe it will help you in your career as a psychiatrist, but it is not absolutely necessary and may even come off as defensive or off topic if not done properly.
It is not a question of "standing out" as much as it is a fact that you should ensure that every controllable portion of your application is at peak potential. Follow Dr. Toaster's 10 easy steps, and you have a plan:
1. Take the COMLEX Step 2 and the PE early enough that all scores will be back by the time ERAS opens for application submission. You'll be in a better place with Step 1, Step 2 and the PE all back and posted with the rest of your application. It makes you a safer bet. If the program requires the USMLE or you have opted to take the USMLE too, make sure those scores are all back as well. If your scores are not in by the time applications are initially open, programs may e-mail you to ask if you have taken it and what your score is before they offer you an interview, or you may be asked about it on your interview day. If your scores come in during the season be sure to "retransmit" your transcript via ERAS. You will absolutely need to have Level 2s done by rank time as many programs will not rank you without them passed.
2. Send four LORs - period. Many programs only require three, but you have no idea what is in the letters. Four gives you better odds that a blah LOR will be outshone by a better one. On the same note, ask for letters from a variety of writers (i.e. if your OBGYN preceptor loved you, then get a letter from her/him). I feel like the perfect combo is two Psych (one should be a chair letter) and two other (IM, Family, Surgery, whatever is going to be full of strong content). If you do not have a psychiatry chair at your school, as is common for many DO schools, your preceptor letter should be fine.
3. Use your extracurriculars to paint a picture about who you are as a candidate. I most certainly did not write down every single project or volunteer thing I did in med school. Instead, ask yourself what you want the application to say about you. For me, I wanted to show my strong commitment to teaching and add in the quirky flavor of my non-science/medicine related interests. To do this, I actually did list a couple of extensive college extracurriculars (amounted to hundreds of hours), and I filtered my med school experiences.
4. Spend more time on your personal statement than you think you need. Have many sets of eyes read your personal statement. Go through drafts. In all seriousness, I spent about two months working on my PS, went through 4-5 drafts and had no less than ten readers (friends, physicians, mentors, etc). Your personal statement is your introduction to the committee, but it is also a chance to add more cohesion to your application. It should complement and enhance your ECs and function as an outline for the topics you want to discuss during your interview. As a final note, don't write too much. Limit the PS to one printed page.
5. Use your "Hobbies and Interests" section to be a little more casual. You can write what you actually do. If you love fly fishing, cello covers of metal bands and making your own pasta, SAY SO. Literally every interview I went on involved some reference to my H&I section; it was always a conversation starter. One PD told me that he looks at that section before anything else on the application since it can say so much (or so little) about a candidate.
6. Maximize the temporal control. Have ERAS ready to go before it opens. Hit apply the day ERAS opens. Have your contact email forward to your phone, and reply to interview invitations ASAP. I scheduled many an interview while "on a bathroom break" during rotations. My average turnaround time from invite to getting something scheduled with the PC was less than 30 minutes. Plan your boards so that all scores are back before ERAS opens; if this isn't possible, remember that COMLEX scores have to be retransmitted to generate an update.
7. Do not schedule interviews at your top programs at the very beginning of interview season. My top three programs were scheduled mid-season, and that worked out well. Your first few interviews will be a little awkward. Your last few interviews will be a bit bland.
8. Schedule as many interviews as possible. Attend as many as possible. Do not feel safe. Expect to be tired by December, but push through January. You'll be happy once you get to the end and have the luxury of nitpicking. As a corollary, you also may not realize what is important until partway through the season, and you want to be able to cut a program that doesn't fulfill your needs (or cut one where the PD doesn't show up on interview day, ahem).
9. Make sure you have a real reason (or set of reasons) for picking the program you are interviewing at...at least by the interview day. These reasons can be anything, but be sure they are genuine.
10. Be very careful at the interview day (and at the dinner the night before). You do not want to be "that candidate" who won't shut up, brings every topic back to themselves or just can't interact like a normal person. You should be yourself and be genuine, but more of the version of yourself you might be when meeting your significant other's parents.