I know that it is extremely competitive. It's not necessarily the hardest PI, but the most people want to do that one most, so it's competitive. The more experience you have, the better. And they look for leadership experience/qualities so try to maximize those in your resume. Networking is also very important when getting these. Try to set up a job shadow or something to help meet people.
I never really applied, mainly because I knew I hardly had a chance and because I'm not really interested in that sort of management. So I don't really have a lot of first hand knowledge, however in my current role I do work a lot with management as well as the PIs. Good luck!