Quoting from the new Guild FAQ in the Entrance Hall:

Quote Originally Posted by Guild FAQ
Promotion to Member
Promotion to Member is based on participation, conduct and contributions in your posts. Quantity of posts doesn't matter - you could be promoted on the basis of one amazing post, although just showing the ability to interact with the membership in a helpful and polite manner is easily sufficient. In other words, you don't need to do something special, just enjoy yourself whilst following the Forum Rules above. Although introducing yourself (if you have not already done so) in the HAIL New Members! (Introductions) thread doesn't hurt.

Promotions are handled manually by the Guild Staff, and are generally done en masse. So as a very quick rule of thumb: if you've been here for a few weeks and been posting reasonably regularly during that time, you should be promoted to Member.

In any case, the staff will always try to help you if they can. If you feel perhaps that you've been mistakenly overlooked (as does happen on occasion), your best bet is to PM KukriKhan and explain your situation.