When Barry uses his super speed, whatever happens, it has to happen FAST. The moment the film starts taking place from his perspective, the whole movie slows down. So what may take about 15 minutes of screen time may add up to about a minute or two, maybe even less, of his whole day/personal life, so the filmmakers should keep that in mind. Like if the film were nothing but non stop action of Barry as The Flash from start to finish, it could begin with him getting to work at like say, 9:15 AM, and then end with him returning to his desk at about 9:17 AM, we will have experienced an entire two hour adventure in the span of two minutes. That is one of the beauties of The Flash and what makes him so great. That's where the "Back to the Future" feel comes in, where Flash and the audience are having this huge adventure, but the rest of the world will never know it.
(^^ The Flash vibrating the molecules of an entire plane through a bridge would make for a fantastic scene in a movie ^^)
THE VILLAIN - MIRROR MASTER
Although the movie needs to be about the hero more that the villain, I think Mirror Master would make an interesting choice for the villain in this film because one, there aren't any other villains like him in comics. Coming out of mirrors/reflections would be cool/creepy, his powers are unlike that of any other comic book villain, and he is able to negate The Flash's abilities and be a true threat to him. He could also be really scary of done right. Basically, Sam Scudder, the man who becomes Mirror Master, is driven insane by the weapon he's stolen/his use of it, his evil taken to its fullest potential, but the viewing other mirror worlds and things makes him mad with power. He kidnaps people through mirrors. He can find the prettiest girls all over the city in front of mirrors/reflections and kidnap them, he can really be anywehere. He gets a gleeful chuckle at how narcissistic people are, and just when you're not looking, he is there.
Sam Scudder aka Mirror Master should be kinda a lowlife felon (well, maybe slightly above your average thug), he'll be out of prison, his first murder is one he where he killed a victim with a mirror of all things, he is only referred to as "Mirror Master" once in the film (maybe a self referal, if at all...), and cops or people nickname him "the mirror man" when he is mentioned. Anyway, he should be an almost average thug who stumbles on to the technology and uses it to commit petty crimes at first, but his mind becomes "broadened" so to speak by the mirror realms he inadvertently "dicovers" and eventually he becomes tainted and completely power mad, possible plot could be pulling the entire Central City into a Mirror realm towards the end? Like a giant stunt.
Anyway, Scudder is a "reflection" of Barry Allen in a way, as he is a "blue collar" thug initially, the same way Barry is a sort of "next door, average guy", but a cop.
The film's climax could revolve around Mirror Master using a giant mirror weapon that is going to use the light of the sun or some light beam like a giant reflection to pull the entire city into a mirror realm (it is also here where it is hinted at that there are "other realities/worlds" out there, which will become a mainstay/theme of The Flash franchise and explored in sequels by Barry Allen), and we get to see just how FAST Barry REALLY is, as he has to run into the mirror realms before they seal up and pull the people Scudder has kidnapped out of it, AND find his way back out every time....every "reflection" leads into a whole different mirror world, very few kidnap victims are in the same "reflection". Even if there is more than one person in a "portal", he will have to go back for them because he does not have super strength and he cannot carry them all. This will be a real challenge for The Flash. Meanwhile, time is ticking away, and once everyone has been taken OUT of Mirror Master's mirror realms, Barry is going to have to escape before it closes up, and he is going to have to out race the reflection in order to do it, he escapes narrowly. He tries to save Mirror Master but he wants to live in his realm, refusing to leave, because that is the "real world" and everything else is just a reflection. Mirror Master unleashes the reflection beam that travels faster than the speed of light and in order to prevent the city from getting sucked into it once it bounces off Mirror Master's mirror thing, Barry must catch it. Barry can't save Scudder as he jumps into his mirror realm as he fires the weapon and Flash makes the decision to save the city instead of going after Scudder. Now it could end with him getting sucked in and as he tries to escape the mirror breaks and he is scattered all over the place, and Barry collects the pieces, and one day, if the Mirror is reassembled, piece by piece, they can get Scudder out (who is fine, just in a suspended state since it broke mid jump). Personally, I think that would be best, I don't want to kill him off so he can be used in sequels and team up with the other Rogues to go against The Flash. Or, perhaps he could "escape" or get "trapped" in the mirror ("die" for all intents and purposes), and if the Mirror Master IS to team up with the Rogues down the line it could be a new Mirror Master Captain Cold enlists the help of, like he gives a mercenary partner the technology once he steals it and he becomes the new Mirror Master, new style and everything. That may be thinking too far ahead, but it's just a possibility.
Some of Mirror Master's mirror realms are horribly nightmarish and scary, there can also be little nods to classic Flash covers when The Flash enters in the mirror worlds where in one world he could have a giant head, and in another he could appear as incredibly fat, a little homage to some classic trippy silver age covers.