Since this is my Blog and after a conversation I had last night my the shift supervisor at my current job a few ideas came to me about what DC needs to do in order to make a Justice League movie and make the same successful lead up to Avengers.
You see Avengers is a brilliant movie but the movies leading up to it were the foundation and the main driving force to its success. DC needs to do the same thing if they are going to merg films for an assemble film with their characters.
So what do I think they need....
Superman needs to have a second successful film to prove to the audience that investing in this character and the unified world as a whole is worth the time. Iron Man 2 was the kicker that started off the end game run for Capt America and Thor. If Iron Man 2 failed, those flicks would have died off quietly in the night and Avengers would have never been anything but a dream.
Superman 2 has some unique problems do we deal with Lex Luthor or another Space bad guy? If they go with space with a villan such as Braniac... they can introduce (or re-introduce) the Green Lanter Corps.
As one of the big three, they need a successful Wonder Woman film to make up the Justice League film. It's like having the Avengers without Hulk, Capt America or Hank Pym... ok the last one is a bad example.
With a second film outside of Batman, the idea of the Justice League could be then real. Like Thor, Wonder Woman has magic that needs to be introduced and like Thor her people have been on our world for many years yet we only now know they exist because of Wonder Woman.
Ignore the last Green Lantern and re-boot.
Like the Ang Lee film, start again. Do a Incredible Hulk, re-boot and tie it in as needed.
That's it. Green Lantern sucked it had some moments but moments a film does not make, let alone make good or do justice to a semi-popular and well liked character.
Be ready to Intro Characters in the Film itself
Flash, Cyborg and Martian Manhunter there are a slew of characters with ties to the Justice League. With all the Cartoons and Comics and all the versions you'll need to introduce some of the more 2nd tier characters with Justice League... they could their own film after the success of the Justice League. Of course doing so should not mean a full intro-backstory for the one or two characters in the flick.
Black Widow and Hawkeye were both shown off in other films before Avengers and their backstory has yet to be given. DC should take note and focus on the film as a solo outing that is leveraging the previous successful films.
Figure Out Batman
This is a key part and the last one. Figure out the ending of Dark Knight Rises or ignore the Nolan trilogy. Does Robin take over is Bruce out for good. Does Bruce come back... figure it out and stick with it.
Do you need Batman... yes because the rest of the film will need to leverage the icon and power of the character's brand as the rest of the JL team is pretty limited in prominence in popular culture outside of failure and 90's TV series (aka Flash TV series, which was awesome for its time). The big three are called the big three for a reason.
So DC. If you want your JL, you better figure it out.