I guess you need to be knowledgeable enough with social media campaign. It's not simply all about posting your products and services but you should know also on how to target your audiences and understand their interests and demands.
Agree with Aspen, added to this you should be creative enough to understand the behavior of customers as we can't see them to judge their expressions.
i'd agree with the earlier posts. more concretely, i'd suggest acquiring an in-depth understanding of facebook targeting and google analytics. prove to a potential employer that you know your stuff with these two platforms and you'll have a good in to most online marketing companies