I answered an ad asking for help with a clinical research study. That lead to an independent project within the same department.
For the first study, I was involved with identification of participants, verification of eligibility, enrollment, performed study measurements, outcome tracking, and data processing. I did a lot of grunt work, but I also saw how difficult it is to work with "volunteer" participants (even though we paid them they were not very compliant which kills the data).
For my "independent project", I designed the study, did the lit review, collected the data (chart audits, mostly), programmed the statistical models, and did the analysis. I'm currently writing the first draft of the manuscript. I also did all the IRB documentation. I had a LOT of hand holding from my mentors: an MD and a PhD.
Both experiences were/have been great. I have a much better understanding of the processes and challenges of medical research.
I do have some ideas of what I'd like to work on during medical school, but that's going to depend in large part where I get in. Hopefully that school will have some faculty doing research in an area where I can join/piggy-back a project.