Write pitches. If you have located a client for whom you want to write, send pitches, which are topic ideas for articles. Write pitches that not only show your expertise, but also demonstrate your enthusiasm for the topic. First, read the publication to which you are sending pitches to familiarize yourself with what they publish. If applicable, identify a specific section and send our pitch to the appropriate editor. Also, include a brief summary of who you are.
If you have pop-ups and optins on every page, I would have to think that it would be a lot harder to convince someone to link to it. Especially since the pages where you have your optins (and probably receive the most traffic) are probably the same pages that you have your best content on as well that you'd be hoping to pitch in your outreach campaign.