Forum marketing just involves going to forums and posting useful topics and putting your website link in your sig,you just join a lot of forums i suppose, but to be honest i don't think there is much more to it than that. I know there is probably software that automates it all for you and you could just go and spam tons of forums,but i don't think that way is a long term thing,plus i just don't think it's right. You want to add helpful and useful topics and replies which will then build up trust and a relationship with the members. Was that what you wanted to know?
The key here is to really be ON-TOPIC and try your best to offer honest opinions. If you go into the forum with the mind-set of marketing, you're probably already headed toward a bad path... I'm sure many will laugh at that last statement, but I happen to believe it... The truth about motivations always comes out.... IMHO.
put links in your sig talk alot and be useful = many people seeing your stuff I've also seen others directly marketing their site on here. You'll have to dig around but post it where it should go otherwise admins will growl
If you're relevant on the forums and people get to know and like you, then they will visit your site. If you're asking how to advertise a forum then web directories and having posts/articles worth linking to are probably the easiest things to do.
I found the best type of sig-file is one that draws curiosity with a call to action tag. Example: Exposed: Zero to $2,000 in just 10 days ... Here's How The first part makes then wonder, and the "Here's How" is the call to action. In this case to click for more information on how I did it!
It works best on forums where more newbies tend to hang out, but a lot of others still click through because they think they might miss out on something. But I'm sure many other do just ignor it.
There are more chances of clicks from the newbies as they tend to look for more info than matured people IMO. If the ads are quite relevant there are more chances of clicks.