Posting insensitive jokes and content
There's a fine line between social media humour and sheer insensitivity. It's basic common sense - if you feel like your meme evokes a social issue, don't post it.
Hard-selling content tone
We don't want salespeople constantly bugging and pushing us to buy their product, right? Sometimes, it's best to keep a neutral, conversational tone instead of saying something like, "Why don't you try Product A?" or "Hit the link so I can discuss more about our product."
While it's a common strategy for marketers to buy a number of social followers, this is equivalent to saying you bribed people to buy your product. It's better to have just five followers constantly engaging with your pages, than 500 bought followers who aren't even doing anything at all.
Not using hashtags
Hashtags help your post become more discoverable and relevant. And if you're on Twitter, you can even pay for a promoted trend.
Limiting yourself to just one platform.
Facebook isn't monopolizing the social media sphere. There's Twitter, Instagram. Even Tumblr. Diversify your platforms, and invest in sponsored ads in each platform you sign up.