The same way you get to Carnegie Hall: practice, practice, practice. In front of a mirror, in the shower, whatever works for you. Practice walking through your resume and telling your story and practice answering some of the common interview questions, both fit and technical. And if you can, do mock interviews with friends and ideally, folks in banking. Even better, if you have the opportunity to schedule interviews with a number of firms, schedule the less desirable firms first and use those as practice. You want to get to the point where you can comfortably interview but without sounding too rehearsed in your answers.