In any forum/website's success, the features that I find key are:
- Content. The forum needs to have something that draws in users and keeps them there, because of the quality of the content. Pokegym may not have had all of these things in the beginning, but when I saw it, I was instantly hooked because it has the Researching Tower, a massive community of skilled players to ask about cards, and a wealth of other information, as well as being up to date on TCG news. [I love the Researching Tower.] Don't forget the Trading Forum!
- Community. The most active members must be nice and helpful. Otherwise you're just going to scare people off. It also looks better for a forum to have lots of members even if not all of them are active.
- Advertising. It does you no good to have a forum if you don't tell people. And don't just tell people, don't just put a link in your sig - talk about it. I would have never looked at Pokegym if I hadn't heard so many TCG players talking about it, and I would have never looked at HeyTrainer if I hadn't heard all of the random discussion about it in the RTC.
- Finally, staff. The staff must be dedicated, generally badass, politically fluent, and all-around good at their job. Again, if you aren't, you're going to scare some people off.
There's also more than a small measure of luck.
Pokegym has awesome content, a good community, FANTASTIC staff, and its size gives it excellent popularity and therefore advertising. Hence its size.
