In the Spirit of Sly Flourish and the Lazy Dungeon Master I would suggest starting with the characters. Hunted/Monitored and Psychological Limits can seed half your sessions - this will also tell what the players expect. An Alien Invasion (JLA) Subterrestrial attack (FF) Demonic Invasion (NTT) Trickster God (Avengers) Superpower Terrorist (X-men) Shadow War (BtVS) missing Hero team (New X-men) expansion of a Global Team (JLE) rescue of escaped alien captive from kidnapping (NTT) rescue of experimental subject (YJ) Base provided to heroes by Benefactor (NTT) heroes approached by Insurance company to protect insured customers (Northwind)
Run a session and see which direction the players go.
Think of three things that the heroes could do - five places they might go - three days interesting thing about it each location - three groups on individuals they might meet - five pieces of information.
keep doing this and the campaign will grow