ROI has 2 meanings:
Return on InvestmentReturn on InfluenceContent Creation X (*Social Media + SEO + PPC + Email) = traffic to your website/blog
(*Social Media has multiple purposes, building relationships, customer service and much more)
When you create content you have something to talk about. When you have something to talk about you have a reason to drive traffic to your website / blog. Make sure you are adding value and that you have a compelling call to action when people arrive.
The next part of the formula is to track your conversion on your website. I use google analytics to track visitors. 5 buyers / 100 visitors = 5% conversion.
In a Nutshell: Add value – Drive traffic to your website, have a CTA and track conversion.