I just went to other forums along the same theme as mine and had details about my site in the signature. I also went to completely different themed forum and got to about 10 - 15 posts then PM'd the top dog asking them if I could make a post about my forum on their site (makes you look better if you ask first and they are more likely to say yes, just because you asked).

An introductions area is a good place to start, it is a good ice breaker (or you could hire a fat penguin *boom* tish) and gets people talking.

If you give me a few details about your forum (what it's about etc.) I will add a part to our monthly newsletter (sent out on the 18th of every month) about it. Also I will add you to our links directory.