Well, as you already understand the importance of quality content, you are already half way through my friend. :)
If your content adds value to the lives or businesses of your visitors, it all boils down to taking this content out and reaching to consumers.
SEO, as I assume you understand, plays a very big role here. Let people find what they want at your niche website.
Other than that, using old school email marketing is the best way to induce customer engagement with your brand.
Collect emails through opt ins and engage them through emails. Your quality content would do the rest.
Other than waiting for the customers come in, you can reach them out using Facebook pages and twitter, whichever you are comfortable with. Let each post be helpful for your audience and include links to your website.
There's a lot more you can do and this is a pretty wide question.
If you want more details or solutions customized to your case, feel free to drop a message. :)