I have been a Moderator, a Global Moderator, a Staff Member, an Administrator (kinda[giggle])...but I don't see how that has to do with anything, heh.
Generally, the staff members will select you, you don't select them by putting in applications of the like. Simply post in the forum and sound interested. When I used to staff, I looked for people who seemed like they had a decent head on their shoulders, knew how to post properly to not make my forums look bad, showed natural leadership, etc. So in otherwords, just mind your infractions, don't post if you have nothing to add to the subject (spam), and if you see problematic posts, report them using that
button. Just by those reports alone, you are more than likely going to show that staff member that not only are you interested, active, but also competant in judgement (biased on what posts you report.)