Facebook, Instagram, Snapchat, Twitter, Pinterest—we're in the age of social media. So how about harnessing that power and influence to reach new customers? "Social media is where people spend so much time now," says Janelle Warren Konowal, who relies heavily on social-media channels to promote her Nova Scotia–based school, Element Dance Studio. But changing trends and algorithms can make it harder than ever to reach your target audience. If your social-media marketing isn't returning the results you'd like, you may be making some of these common mistakes.