follow the rules, if the URL you want to post is relevant to the thread then it will probably be allowed, if you just keep joining forums for the sake of promoting your website without adding any value to the forum then its classed as spam
Hmmm, there is one strategy I'll mention, but there is a lot of contorversy surrounding it. I generally believe that if you're trying to use forums to increase rank, you're not going to get the results you want by posting the odd link here and there, you have to do it on a mass scale. Unfortunately this would entail spamming. There's a program I've heard of called xrumer, coupled with hrefer you can find lots and lots of old forums that are dead and no longer moderated so you can get away with posting a link. Apparently there are 1000's of dead forums like this, so finding places to put your link shouldn't be hard. This isn't something I've done and can verify. I will say, "proceed at your own risk", this is considered a blackhat method.
New to the forum. I guess that classifies me as a "Peon". Either way, it is good to be here. Like mentioned above you actually need to become an active, contributing member to a particular forum's community. Just like everything else it just takes time. My advice would be to read the Forum Rules, abide by them and just actively participate in conversation. Spam bot options are just a short term solution. If you are truly trying to build links for the long run and for something that you feel is valuable, I think this is the way to go.