Listen, ... keep listening. There are multiple roles for listening in social media marketing:
1) To learn.
You want to listen to as much advice as you can get, but make sure you can weed out the "guru" lessons and listen to people who are sharing real expertise and experience.
2) To find out what your target audience really needs.
What are they complaining about? What do they talk to each other about? What real issues can you solve? Once a colleague mentioned that she listens to what competitors' customers are saying about the product/service.
3) To improve your customer service.
Validate a concern and try to figure out a solution that can be beneficial to both sides.
4) To make social media SOCIAL.
If you're just posting content on Facebook then you've essentially got a digital billboard. And no one goes to visit a billboard to see what ad is up today (unless the ads are amazing enough to warrant the visit). So you've got to stop focusing solely on a "content strategy" and think about your whole strategy. That includes responding, commenting, engaging. Businesses are told that an important social media metric is #engagement; well if you want engagement, engage! And that starts by listening.
If you want to learn more about how to leverage social media listening for successful social media marketing, take a look at Part 4 of the Social Media Marketing Basics Series.