The Flash has not been treated well in Hollywood cause he's been stuck in development hell for so long that at one point, everyone thought the project was dead. Warner Bros still has David Goyer's script on the shelve and Man of Steel's success looks to be giving us a DC Cinematic Universe. It also looks to be with Man of Steel sequel being fast tracked and said to be "kicking the tires" for the Wonder Woman and Aquaman films, I think it's safe to say Marvel's strategy is being used it's funny cause I always thought it would be the safe way to go and the best. This being said, here is I would approach a Flash film before Justice League.
Most well known version
While I've heard that Man of Steel is "the Iron Man of the DCCU", I feel that title should belong to The Flash cause his film should be the more fun of the movies leading into Justice League. Barry Allen, for me, has always been the most interesting of the different versions of The Flash. He's the average guy who is just late to everything cause he's slow. I think that the film needs to explore his development as a character. His relationships with other characters, his gaining confidence, his reactions to what it's like to be able to do everything super fast and how this new found confidence and these now found powers affect him as a person and the people around him. Not to mention the movie should explore the loss of his mother and how it led him to become a forensic scientist. It should be a mix of character driven story like The Dark Knight trilogy and the action and spectacle of a Marvel film (completely off topic but, those films aren't style over substance overall, just saying). When it comes to his powers, he learns he can obviously run fast and everything fast (poor sex life lol just kidding), the only other power he discovers is the ability to vibrate through anything.
New 52
As Marvel did with their movies in the Marvel Cinematic Universe by basing their characters off the Ultimates mostly and how Warner Bros did with Man of Steel with the New 52. I feel the DC Cinematic Universe should be basing their characters mostly off of the New 52 (I'd still have Iris as his love interest). Even including that when the suit comes out of the suit, it goes over his clothes. Although, I'm afraid that actually wouldn't look as cool on the screen. Who knows.
The Villain
New 52 Captain Cold has always been my choice for the villain in The Flash's debut film. He's much more of a threat and a more interesting character than the classic version. To go with the whole "he's more of a threat" comment, he actually has powers and can be a challenge for The Flash cause he can slow him down. My idea for his involvement in the film would be based on the New 52 version and that his sister is dying of cancer and he would want to kill The Flash for everything including the potential death of his sister. But (and I know this isn't in the New 52), he also decides to steal the money to repair the laser to save his sisters life. Despite the fact that Captain Cold has been trying to kill The Flash (and this would also explore Flash's powers, more on that in a bit), Barry must decide whether to let Captain Cold go or not after learning about his sister. I thought that would be the best and most interesting way to do the debut film. As I said before, character driven but with the spectacle of a Marvel film or as other people on this site have put it. Make it the most "Marvel" of the DC films.
Get rid of Goyer's script
Before anyone says anything, this has nothing to do with Man of Steel. I won't comment on Man of Steel due to the fact I have yet to see it and won't judge his writing based on that particular film. It's the rest of his filmography that worries me. I love the Blade movies (Trinity is more of a guilty pleasure) but, they're more style than substance, The Unborn was not good in so many ways and he's getting only half credit from me for The Dark Knight trilogy. Question is, how much of the writing did he actually took part in. The Unborn just flat out sucked. I wouldn't want him anywhere near The Flash. If you were to use his script, I would do a revision.
I know it's very brief but, this is the basic logic that I have about this. What are your thoughts?