Entries to the ArcGIS Online Competition for US HS+MS need to be either "presentations," "web apps," or "story maps." There are various pointers to each of these, and more all the time. As I encounter more, I will add to this list, and encourage you to reply to this post with other publicly visible helping hints.
General:
Presentations
Web Apps
Story Maps
I just added a new section "General" to this discussion because there are some excellent guides for making good maps in the first place, the raw materials to be turned into presentations or apps or story maps. Exploration encouraged!