The way to succeed with your art marketing in this connected era is via sharing.
The "online economy" and indeed the world wide web itself was built upon the premise of sharing.
We share links. We share stories. We share blog posts. We share photographs. We share ideas. We share tweets. We share thoughts with each other. We want to share images of artworks with each other (at least when the artist doesn't use those annoying right-click disablers to attempt to stop us from promoting their artwork for them) And, sometimes, we even string shared series of these thoughts, stories, links and ideas together into what we call conversations
If you want to be successful on Twitter (or Facebook, or your website, or your blog, or pretty much anywhere else online), forget the suggested qestion of "What are you doing?" - Nobody cares what your doing. Instead, ask yourself, "What can I share?"
Asking "What can I share?" puts the focus on those people who have graced you with their attention. It forces you to think about how you can make their lives better.
Focus on making your followers' lives better and, over time, they'll help you make your life better too.