One of the most common mistakes in social media marketing is the use of competitions to grow a page's fan base. If you're a Facebook user then you will have seen it to, a post resembling this:
"Like our page and share this post for your chance to win an iPad."
Seems a pretty solid way of growing a following, right? Probably not. What you're doing is attracting people who are interested in iPads and not your brand to like your page. So unless you're producing content about iPads, then the person who has just liked your page isn't going to engage with your subsequent posts. Due to the fact that the success of Facebook pages is primarily based on engagement rate, every like you get from somebody who isn't interested in your page becomes a future blemish on your engagement rate.
The nightmare is if your competition is too 'successful' and your likes go up by over 100%. This is when your Facebook starts to 'die', as engagement steadily declines and your reach dwindles.
What is the best way to use competitions to grow your fan base then?
Simple. The prize. Make the prize something directly related to your product, or if you want to flirt with the Facebook Grim Reaper then make the prize something that you know your customers like. You might not get as many likes on your page, but at least you know these are healthy likes.
Such a common mistake, but so obvious when you know it.