health related topics tend to do well, tutorials and "how to" topics often do very well also. Pretty much any subject people would want to look up to learn more about - recipes, health, DIY projects, software tutorials, self-improvement etc.
I would suggest coming up with a list and using the Google Keyword research tool to see if it could be a profitable niche area. There are several tools you can use to then SEO optimize those types of articles/hubs to help them place higher.
Use original graphics/photos also to encourage pinning and otherwise sharing socially. :)