Firstly it depends on what spaces are vacant - see the 'Become a Valar/Maiar' forum to see if any spaces are open for applicants. Secondly only apply if you are a very experienced Tolkien fan. Please remember its not all just about moderating posts. Some Valar have specific tasks to do such as advertising or being in charge of banned users.
If you are still intent on becoming an admin/moderator then you may also fill out the form below when a space is vacant (as indicated in the 'Become a Valar/Maiar' forum):