Well there is no secret. its all about content and then seo IMO
im using vbseo to do the seo side of things,
www.gamerzneeds.net/forums you will see vbseo in action, the link is in the footer on my site, as im not sure if im allowed to post it here.
as for content, if your not passionate about posting, then it will be tough.
here are a few ideas. create several accounts, and on the other accounts, just post lots of stuff up. on your main account, be yourself and make good original content that people are likely to search for in the search engines.
just because your site is about xyz does not mean you cant talk about another topic that has nothing to do with your site.
good (active) communities have a main focus where people go to get the content, and a place to enjoy the community as well.
Hope that helps.