Rating your best images with a high number so they show up first on the event is a good way to get people excited to see more and they will spend more time on the site.
Doing discount sales periodically will help you sell more prints and with Instaproofs it's very easy to set up.
Use the email function to send mass emails informing people that the event is online, the prints are on sale, or that the event is about to be removed.