It's interesting that many organisations fail to see the difference between "vanity metrics" and things that actually make a difference to the business...
You need to start by understanding your business goals. Your social media isn’t there to serve any other purpose than help you improve your ability to obtain those business goals. Therefore, the social media metrics you need to focus on are directly related to your business goals. If a metric doesn’t tell you how well you are doing in terms of business goals, it isn’t really worth tracking.
http://www.bloggingtriggers.com/social-media-metrics-simple-guide/