ACTOR/ACTRESS: First of all, there should not be any A-list Actors for playing characters that is Batman, Flash, Wonder Woman, Aquaman, Martian Manhunter and i hope Henry Cavill should remain for Superman. The character has to be bigger than actor who is playing which will keep the actor/actress more focused towards the role. other thing is the contract of each of the actors should not be limited for this particular justice league movies coz if this movie is a hit then these actors will be in demand for sure and hard to get afterwards.
DIRECTOR: He/She must be a man with a 'deep interest' for these characters/Movies for e.g. Joss Whedon for Avengers & James Gunn for "Guardians of the Galaxy". The "Interest" part is the thing which made "The Avengers" a Success. my choice: Brad Bird or Guillermo del toro
MAN IN BEHIND: The main reason for the Success of Marvel and not that success DC CBMs is the so called "Man in Behind". Kevin Feige/Avi Arad looks out for the movies plot and details of the movie as they want it to be. they look out for some particular things like sticking to the material as in comic book. for DC they can have Bruce Timm and Paul Dini.
DC-Owned PERSONAL STUDIO: The main problem with DC unlike marvel is that the DC hasn't got their own studio and has to rely on WB. trust me WB don't care about DC success they care about only money which is why the only character you see in the Silver Screen is Batman with an acquaintances of superman and a pathetic attempt of Green Lantern with an awful script. I know this is not going to happen but it will be great if it does happen.
A-list Actor for Villains: Now, whatever you do,you must have an A-list Actor playing the main villain, this formula has been used for decades and has worked successfully or you can find an actor better enough to play that part i.e late Heath Ledger for Legendary Portrayal of Joker in TDK.
Reverse Approach: Now that WB/DC are all set for JL movie which means movie on solo character is gonna be held post-JL. considering it is a success which i hope it will be. Unlike marvel who were concerned about the characters which are not so popular prior to their own movies but Justice league characters are quite popular thanks to my favorite 'Justice League Animated Series'.
So, these are the few points or key things according to me which will make DC as popular in comic book movies other than Batman as like Marvel. hope you like this Article and feel free to comment if i missed any points