I love resident decorating contests! One suggestion - sometimes it is a good idea to have a third party do the "judging" so you are not put in the middle. :) Usually, if the property is sponsoring a contest and awarding prizes the property's budget covers the expense. I would suggest having more than one prize though - sometimes it is nice to give out "participatory prizes" of coupons to restaurants or $5 Starbucks cards to a lot of people. That way they feel happy to have made the effort. Advertise it on your facebook page (but not asking for Likes) and on your website resident page. As for rules, I would go over this with your company - some allow nails in common area hallways, others don't. Take photos - lots! - and put these on your Facebook page and website, too! Put them in newsletter, too, if you have one of those. Have fun!