I have been participating in quite a bit of forums. For quite a long time. From back since 2003-2004, I have been in forums. Not too long, but the participation in the forums did help me launch my own projects, with the help of like minded people I found through forums. Some of the forums I participated, in the rough order of join date:
Aelyria (previously Alleria), got me introduced to forums, when I was actually searching for an online RPG. That hooked me up, and spawned many failed attempts at creating my own RPG - Chaos And Order. But that effort also resulted in me writing a novel (yet unpublished), and providing inspiration for a lot of my artworks. I joined AstaHost and HostBidder to get a webhost and domain name. The result was WiseTome.com and Splat. I am still a toddler in Drupal space, but I am glad I got involved with that community. LoreleiWeb Forums provided me with friends and inspiration for many ventures like CGPainting.com and providing art products and services.
Enough with the background, let me get to something I have learned.
Use Forums To Help Launch Personal Projects
Lurk before you post. Yes - even though, as a forum administrator myself, I would wish lurkers would post early, my honest advice would be to lurk a week or so, when you stumble across a forum and join. This will get you acquainted with the vibe of the community.
Know the rules. Not just the written forum rules and policies. When you lurk, you will notice there will be some unwritten rules. Some things, purposefully avoided. Some customs. Some way of participating in the community. Make a note of such things before you start to indulge in the forum.
Expect the worst from people, but take the positive of everything said. Yes - some people can be jerks. Internet has that tradition of such trolls, ego maniacs, and the odd lots from days of UseNet. It is not a surprise that every forum has a part of its membership filled with such people. Just ignore them, and concentrate on what you came into the forum for.
Do not expect every one to like your idea, or contribute to it. You would have joined the forum with an idea for a personal project of your own. You have a vision, and would give anything to have a handful of people to help you out in it. But remember that the others are in no contractory obligation to help you out. Do not act like a jerk or throw temper tantrums when your post remains with zero replies.
Find common grounds between others project and yours. As I said, it is hard for two people to have an exact same match of ideas. Especially when your plan is grand and elaborate. When such is the case, see what others are interested in, and find smaller things that more than one can work on.