There are no clearcut rules. But what is sure is that at least:
- you must be a CQ
- you must have worked as a Moderator in a number of shows
- you must be an active volunteer (whatever that may mean)
- you must not have too many other projects at the same time
The more popular shows, the ones in demand, are given to experienced Channel Managers who have proved themselves.
If you fulfil those prerequisites, even if a channel has 30+ applicants there's still a chance that you get it. It depends on who the others are.