So first off, I think Man Of Steel will be a huge success and make a ton of cash, which will probaly be the start of a DC cinematic universe!
After Man Of Steel, I wouldn't just jump right into the Justice League.
You have to know and respect the characters and have them have their own movies.
Phase 1, if you will, would consist of:
Man Of Steel (2013)
Wonder Woman (2015) This would show her origin and show Diana, Princess of Paradise Island, chosen to go into Man's World to spread her society's teachings of peace and understanding, while a villain threatens to take control of paradise island or something along the lines of that.
The Batman (2016) I would make this about 2-3 years into Batman's career as a crime-fighter, the villain would be the Black Mask and I would bring killer croc in for a fight scene to show that batman lives in this fantastical universe with all of these other heroes.
Justice League (2017) The movie would start with just superman,batman and wonder woman meeting and trying to understand what is going on, there are tsunami's and earthquake's happening near the Atlantic ocean. The Flash and Green lantern would show up because there cities got hit with earthquakes and want to know what's going on.
It turns out that Aquaman is making all of this happen, Black Manta (once his friend) makes a deal with Darkseid (he wouldn't make an appearance in the film, he is more of a behind the scenes villain) and switches Aquaman's trident with one that ampllifies hit anger and hatred and makes him take his problems out on the humans and causes earthquakes,tsunamis etc. So then Aquaman finds out about the league sticking thier fingers in his business and wants to kill them, he sends his army up to the shore and a huge battle takes place.
The League destroy the dark trident and arthur turns back to normal, they find out about darksied and they want revenge on him, aquaman joins the team and at the end, Superman,Batman and wonder woman are in the batcave, batman is on the bat-computer, they are finding out information about darkseid. Superman asks "so where is he?"
Batman replies " Apokolips!"
END CREDITS!
Stay tuned for Phase 2!