Something that I see quite often is people making a simple but important mistake. They reward the behaviours that lead to quantity rather than quality.
Let me explain.
When you build a gamified campaign or activity, you need to consider what quality participation looks like. If for instance you want to create some buzz around a new product and you decide to create a simple Twitter competition, are you looking for the number of people who tweet or are you looking for the number of people whom the message will reach?