Been involved with Beltline through Planning Group for over seven years now and more recently through Transportation committee. Unlike most other CA's, we look at development on a weekly rather than monthly basis.
As for what works and what doesn't... it's tricky. If you are meeting really late in the development process, chances are that whatever you have to say will have little traction, so getting in as close to pre-app as possible is important (and don't count on the City to circulate you on anything).
Also helps if you establish your CA as really active and wanting to help developers rather than trying to combat them.