Pokemaster hand-picks.
Usually, a Moderator will suggest a promotion. PM fulfills or denies.
If you wanted to get to Editor, here are the steps to take.
1: Good amount of points.
2: Show good questions, and quality answers.
3: Been on the site for a while, and be very active. A good amount of time a day.
4: Show you truly want it. Be a helpful user.