In my experience the vast majority of students who get involved in research and get published work on a project that was conceived by one of their supervisors. Students may have some influence on the direction the project takes, but most students do not have enough knowledge about a particular area to identify something that hasn't been done, or a good enough understanding of methodology to design a project. There are of course exceptions, and if you think you have a good idea, it's certainly worth approaching someone in that area and asking them if they would be willing to supervise you. There are a huge range of possible projects. On my iBSc there are students doing wet lab projects, systematic reviews, analysing data sets, going through patient notes to collect data, there are some who have collected samples from patients that they are analysing in the lab, there are people doing qualitative studies interviewing patients, observing teamwork/communication of healtcare professionals in practice, projects on education and training, and projects on patient safety. It is certainly possible to get a well written review published, but I know very few people who have been able to do this. Most people who get published are either very lucky, do an iBSc, or work very very hard, and often all three.