Use Pre-Existing Communities
"[P]ick and choose other social media sites like Tumblr or Pinterest that you may benefit from learning to use.
For example: I'm writing a cozy mystery series that features a professional housekeeper.
On Pinterest, I interact with Flybabies, which are women that follow an author's housecleaning system (the Flylady) - an already built community I can tap into my pinning that content, curating it with my own comments on how it relates to novels' sleuth.
On Tumblr, I also tap into an already-thriving community: Caskett shippers. Don't worry, not peddling necrophilia here: that's a 'shipper (as in relationshipper) name for Castle and Beckett on the cozy mystery-esque TV show Castle. By understanding the culture of different social media tools and tapping into pre-existing communities, I forge connections without forging the wheel ;-)"
This works for not only fiction, but anything you're marketing. These two rules have led to plenty of success and plenty of time saved in my social media efforts.
Hope this helps someone :-)