Consider your objectives
Who are you trying to get to enter your contest and what is the objective? Is your goal # of entries or is it awareness about a certain product/service? Establish KPIs from the get-go so you know why you’re running a contest.
Know your contest’s channel – channel: singular!
There’s no point creating awareness about a Twitter contest through a promoted Facebook post. Target your message to the appropriate channel and ensure the contest message feels native and authentic to your channel.
It’s also easier to run a contest on a single channel, from an entry collection process to general participation. Don’t dilute it by including more than one social channel. It you’re running a hashtag contest on Twitter, don’t also include a Pinterest entry mechanism. Determine the optimal place for participation (comment, UGC photo) and select your channel wisely.