To answer the OP's question, I would have to go with forum posting and blog posting.

Adding a blog to your website about your site's topic adds good, quality, fresh and frequent content to your site and it also demonstrates that you're knowledgeable in your field. Additionally, it serves as "link bait" ... content that people are naturally going to be drawn / want to link to.

I am also personally in favor of posting on various other forums within your industry when first starting out, linking to your site in your signature. Yes, there might be a little hint of SEO benefit (no one really knows whether forum signatures do much nowadays), but you're going to get your name out there among other people in your industry as an authority in your field. (Just make sure you're posting quality content!)