Criteria to become a local board could change base on it demand and theymos preference to it at that particular time, but on a normal, one have to be an active member of the forum, report posts and have high accuracy of his reports, after fulfilling all these, it depends if there's a need for a moderator or not on a particular board and whether theymos announced for it or not, before you can know the next thing to do, whether to push forward your application or to even hold on till there's a demand for for such.