Sure. Global directories aren't my specialty, but have you done the basics?
Keyword research. What keywords are you wanting to rank for? I assume you're going for individual cities like "Atlanta chiropractor." Do you have a page for each major city you want to rank for?
Competition. Have you researched your competition? What are they doing to rank their directories in each city? How can you improve on what they're doing?
Backlinks. For a global site your backlink profile is pretty weak. You may want to consider building up referring domains through guest posting and other legit avenues. Research your competitor's backlink profiles.
This is a big project, I'd suggest concentrating on ranking in a couple of target cities first. Then take what works and apply to other cities.