When you say that you're interested in social media marketing, what you really mean is Facebook marketing. At least, that's true in most cases. Facebook is a juggernaut, the clear social media leader, and it's been that way for a decade.
Why is this? Why did social media sites in the past rise and fall, but Facebook seems to be here to stay? And, if you can find an alternative, would that give your advertising an edge over the competition? It's crucial to answer these questions when deciding what approach you want to take and how it may need to change in the future.