There are many different ways that you can promote your project, and this is by no means a comprehensive list.
Your project summary page is often the first impression that anyone has of your project, you should, at a minimum:
SourceForge projects have the option of a blog. You may already have a blog for your project, but we encourage you to post to your project blog on SourceForge as well - particularly when you do a new release. This brings your release to the attention of the Community Team, which then triggers various promotion activities on our side, including mentioning you on Twitter.
Whether you host your project website on SourceForge or not, be sure to link to it from your project summary page.
You need a place where users of your software can come talk. If you don't have a discussion forum, you are telling people that you're not interested in what they have to say, and they'll find another project that is. Discussion forums are a great place to figure out what your users want in the product, to find new developers who want to help you, and just to get a pat on the back for a job well done.
Open Source is about community. From good communities comes good code. Be sure to give your community a place to talk with one another.
If you want to promote your project via any of the SourceForge communications - our blog, podcasts, or our monthly mailing - just tell us. We're always looking for projects to write about, or interview, and who better to talk about it than you?
Also, each month, our community mailing features projects that are looking for new developers, either to rejuvenate a project, or to fill specific gaps in the team. We'd love to feature your project there, too.
Our podcasts are 10-20 minute conversations, conducted over Skype, about whatever you want to say about your project. We try to do one a week, but we depend on you to provide that content. Don't hesitate to contact us.