In fact I think that "skill" is the least important, just participate, there isn't much explanation in those contests, I think the key is to do "something" and you're already participating.
If you are interested in participating then skill is not important part in these competitions as you can come up with anything but if you want to have winning perspective then you need to be creative and show your skills in them.But main is participation in then if you want to take part in such giveaways.