Submitting to all major social bookmarking sites and even micro blogging services. Including the link in forum signature, submitting to directories.. will surely help you..
But befire that try to add some content to your content so that people visit your forum.
If you want to promote your forum then try to get some banners up on some relevant forums that will give visibility to your forum. Also, putting signature links in other forums, creating a community on social networking sites and letting the members know about your sites could help you to get visitors.
A good way to promote your site is deligence and time. Go to the search engines and submit your site for indexing. Post in social media, especially Twitter and G+. If you have a blog, set it to auto-post to Twitter, Facebook and or G+. Try and get articles written on other blogs, and link back to yours. Stay dedicated. That is my advice in a nutshell :)