EDIT:
According to the FAQ Home under Tiers, advancing to the next Tier requires a qualifying Average Score AND a minimum amount of completed stroke play games. WGT has never divulged those numbers. Master tier players can weigh in on this to give you an approximation if you are curious.
My advice is don't be in too big of a hurry to move up...if you play out all your rounds, play all the courses and throw in some 18 hole rounds, you should naturally be in the tier where you belong. We all know there are artificial things a player can do to move up quickly, but many of those soon wish they were in their old tier again, but there is no going back.
Joey