Firstly it depends on what spaces are vacant - see the 'Become a Valar/Maiar forum to see in any spaces are open for applicants. Secondly only apply if you are a very experienced Tolkien fan. Thirdly email The One to request to become an admin or moderator. He will probably ask you an in-depth question which will need textual evidence and extensive knowledge to qualify. He will then judge if you are of Maiar or Valar quality.
Please remember its not all just about moderating posts. Some Valar have specific tasks to do such as marking tests or being in charge of banned users.
If you are still intent on becoming one of the powers then fill out the form below: