You can’t really do anything to improve your application if you mean starting new activities. What you can do is go over the websites of the schools you’re applying to, including course catalogues if you can access them, and figure out how you fit into this school and what you bring to the community. Then craft your essays and application to show that for each school.
We are trying to impress on you that with schools this selective there is an element of luck, or some unknown factor, that no one can predict. That’s why we advise applying to more schools.