First,
You need to promote at this link here on FP:
http://forumpromotion.net/viewforum.php?f=3
You also will want to keep people up to date on your site, i.e. news events, new additions, what is hot or not...
Advertising/Promoting at several promotions sites is key but be careful. You want to choose the right promo boards like FP. You need exposure so go with the sites that you find to be active and offer sound solid services. Be wary of ones that boast of being the absolute best... most of those are dead boards and are far from being the best. Look to see if their is board trashing on those sites, if there is, stay away. Drama on Promo boards is bad news and you simply do not need to be part of it. Your on a promo site to get your site known not get into board drama wars. Admins that do clean those type of topics up are not going to be any good for you.
FP, The Admin Zone and phpBBC are very good boards.
Work with similar sites as yours and do affiliate exchanges. you may want to request a few post packages as well to get your board topics active.
Make sure your style is good on eye and that you have content. No content, no members it's that simple. Some will forgive a poor style if the content captures them, others will not.
All and all, get out there and tell people about your site and do it in the right places
🙂