One of the things that always impressed me on my old forum up in Michigan were the sticky threads that were placed in each particular section of the forum, written as an article by someone in the forum outlining the basics of everything one should or might want to know about that particular common topic (i.e. ich, cycling, personal safety re: electricity and co2, what to do in a power outage (alongside the emergency contact list)), locked, and posted as a sticky thread in the relevant section. I think it would be fun to gather a few volunteers, pick a few REALLY common topics that could be covered, and do some write ups. In a few cases, we could probably replace an existing sticky thread with just a really straightforward article!
Some of the other REALLY good topics were
-Things to consider before buying a tank
-Acclimating new livestock
-Aiptasia (always with the Aiptasia!)