I don't want to be an instructor particularly, but PADI has 2 educational ladders after Rescue Diver. One of the paths has one item on it, and the other has 3. Since I want to continue to learn, the longer path looks more interesting.
What type of diving interests you? Wrecks? Photography? There are tons of specialties you can take for tons of different things, but you can never be certain you will learn a great deal from taking them (ie Night Diver). At the same time, a simple specialty can really pay off (ie Navigation) - depending, of course, on the instructor and your individual efforts. I would suggest that you may want to just ignore the ladder they have all over their marketing materials, and make your own plan.
I think often it's very beneficial to also learn by doing. Learn by diving with people that have a lot of experience and don't mind sharing and helping you out. You don't have to be a card collector to gain knowledge, do you?