It would have to be diver friendly to ALL levels of training and experience, and not be a (even in appearance) an exclusive club geared mostly towards those dive masters / instructors with better than 300 dives loged. And those who do have the higher levels of training / experience would have to be willing to help along and encourage those new up and comers to diving.
Have a very user friendly web page! Something easilly navigated and not too confusing. Per haps have a (monthly?) social gahering at a local dive site, BBQ, diving / training, and possibly even some kind of "An introduction to diving" class / seminar geared towards those who are not yet divers, but would be interested in learning about it with some hands on (supervised) usage of gear to really peak their interest.
Also, for the more experienced divers have some kind of competition every so often, say photo contests, scavenger hunt, etc.. with prizes, mabey that will encourage the rookies to want to learn more and become better divers.
I’m sure alot will think my ideas hee are not practicle or even stupid, it’s just what sprang into my mind when I read this post.