M.R.
My husband has successfully helped many people get in to medical school. It is a little early to choose your field of interest though, i.e. psychiatry.
There are many elements to a strong resume:
1. In your letter with the application definitely mention psychiatry as your primary interest but add a personal story or experience to support the why. Is there someone in your immediate family or circle of friends that has suffered with mental illness and this leaves you with a better than average insight to the trials and tribulations of the patient? Etc...you get the gist.
2. So, will you be shadowing a psychiatrist in your community? Have you set something definitive up? If you can't find a Psychiatrist, then definitely find a Psychologist with a minimum PhD. to shadow. They will be looking for a real serious commitment with a lot of hours, not just a once or twice scenario. Then after that shadowing experience, make sure to ask for letters of recommendations from these professionals.
3. Go to your university and find a research lab in any of the Neurosciences. Either volunteer or asked to be paid, even better for a part time position. To combine your interests, maybe you can find a lab specializing in stroke coupled with rehab research in one of your areas of interests.
4. Contact the medical schools you will be applying to and have them make specific recommendations to your application as it stands right now. They are willing to tell you before hand based upon what you would be submitting what they would want to find in your background to augment your application. It could be more bench research, more clinical studies where you volunteered as the coordinator in a hospital, higher sciences grades, so maybe you need to commit to a Masters degree in a bio medical field, even if you don't finish it, it shows that you are currently working towards it....
Also, ask your own primary care MD their own personal story and if you are a stellar patient and on good terms, they would be helpful with many suggestions. Don't be afraid to ask the doctors around you for their stories of how they got into medical school.. The answers are amazingly varied.