These tips and comments are great, and definitely need to be known. The best thing you can do when advertising in a forum is to make quality posts, and then after you make a good amount of posts advertise your site in the ad area of the forum. If you put the link in your signature and in the website field, that helps too.

It's better, after all, to make many posts in a few forums with your link in the sig than to make 5-10 posts in many forums. You're not seen as a spammer and more of a quality member for the forum that wants to advertise their own site.