Characters must actually talk to each other and work out problems instead of letting them fester or having misapprehensions go unchecked. I know a lot of dramas and comedies wouldn’t work without that premise. Figure it out.
Make sure at least some corporate execs are good guys.
In other words, no more saying “It’s complicated”? 
Mine would be, people using computers must use them in a realistic manner.
TV series opening credits would be different each episode; maybe the same song, but a different artist.
As a Good Liberal, I’m glad to see diverse casting. As a consumer of entertainment, that same diversity can make for more interesting productions.
Too many shows have several almost indistinguishable good looking dark haired white guys. (There was historical reason for this in Downton Abbey, when it was noted that all Lady Mary’s swains looked alike; they put blonde streaks in Poor Matthew’s hair to make him stand out. Writing to distinguish the different characters? Not from Lord Fellowes.)
Actresses also tend be young, white, slim & have the same long hair. At least hair color varies. Sometimes a character is The Edgy One–give the guy some facial hair & let him wear a hat! I’ve never watched NCIS but know there’s an Edgy Young Chick in the cast; does she always dress that way?
I like casts that include different ages, body types, races & degrees of beauty. Let’s have more character actors with interesting faces! Yes, casts will include disproportionate numbers of good looking people; but why must they resemble the Abercrombie & Fitch catalog?
And make them say ‘Goodbye’ rather than just hanging up rudely and continuing their conversation with the other character in the room. This is really common and I always imagine the person on the other end of the line staring at the handset saying ‘At least say thanks/ bye, a**hole!’
Actually all of the above. I can’t pick one. I was going to say the musical instruments and the ‘walk with me’ conversations too.
Another one, on a more serious note, is genuinely crying children. I think I got this from my mother. She always winced when she saw a frightened or crying toddler on screen exclaiming ‘That child is really upset! How did they make him/ her cry? Disgraceful!’ etc. 
Or, when they’re holding the controller, they aren’t just moving the sticks and pushing the buttons all willy-nilly.
You don’t play video games by just randomly hitting buttons and moving the joysticks. Well, unless you’re playing Marvel vs. Capcom 2…but we aren’t counting that…
Sorry, one more. Put heavy things in suitcases to make them hard to carry. Actors swinging suitcases around blithely as if they were as light as a feather destroys the illusion rather.
This always bugged me when watching X-Files.
Another X-Files: One character would walk away/ignore the other one who was calling out their name.
Scully: “Mulder! Mulder!”
Mulder: - - - - - - - ->
Okay, fuck you, dude!
There are so, so many things TV and movie productions habitually get wrong. Sometimes it is simply for time. I try to let time things slide (such as wasting 20 seconds of screen time waiting for a phone to be answered, or turning on a TV and having to wait for it to boot up and find the proper channel). Often it’s for drama (TV and movie characters have more coincidental happenings in an hour than most people have in a decade).
But the one thing that gets to me every time (and I say this as someone who has never owned a firearm and hasn’t held one since basic training back when Daddy Bush was in charge) is how all shows handle guns. Whether it is constantly racking shotguns or pistols to “show you mean business” or the never-ending clips that only run out of bullets except when dramatically necessary (especially with automagic* weapons) or the noise (more specifically, the lack thereof) or any of the other things they get wrong, it suspends my disbelief more often than any other thing. So if I could fix one thing, it would be gun-play in TV and movie productions.
*not a misspelling
No one shall be seen or heard vomiting. We’ve discussed this here before. I don’t understand what it’s supposed to add; I can’t remember the last time I witnessed someone throwing up IRL, nor have I ever lost my cookies in response to bad news or fear. So it’s not only gross but unrealistic.
Nobody should be able to hack a computer unless they can do it like it’s done in real life. Ditto knocking people out.
Yes, Leverage, I’m coming for Hardison and Spencer.
I’m ok with this, actually. I want younger kids to play them too, but I’d rather have those younger kids a) in a normal high school and b) away from Hollywood.
Minor things in movies? I’d like women to act as sensibly as the men do, that is, no screaming for ten seconds or more when confronted with a body. When was the last time you heard a man scream like that at a dead body, unless for comedy? And on the other token I’d like to see the men show a little more normal emotion. When you’re just an accountant you are not MANLY MANLY MANLY, you will scream and freak like anyone else if a body falls out of your closet.
I’d eliminate the following:
*Our heroes are in a desperate situation.
“Wait a minute. I know something that just might work!”
Cut to new location.
“This is the Plot-A-Tron 5000 device. Let me NOW explain my idea.”*
So they drove all the way across town in dead silence so he could explain his brilliant plan only when they got there?
Tires do not make the same screeching sounds on dirt that they do on asphalt. Just stop it.
Came here to post about these movie knockouts. Hate 'em. Just strike someone in the back of the head with your gun, and they’re out for exactly the amount of time you need to further the plot. Then they wake up, rub their head and continue on as if nothing had happened.
Yeah, I can’t stomach movie knockouts anymore. There’s some movie where the lead character gets knocked out 4-5 times, and all I keep thinking is how much permanent brain damage he is going to have by the end of the movie.
Shocking flatlines.
No more empty (and free!) parking spaces precisely in front of the building you’re going to.
Because fuck you, movie and television people; if I have to circle the block three times to find a place to park and then spend five minutes trying to find change for the meter, so do you.
Cocking for effect. In fact, I would insist that there be a firearms expert on any scene involving guns, and that his direction be followed to the letter. But the cocking thing: guy pulls a gun and surprised other guy. They have the obligatory conversation, and the second guy starts to make a move. Guy with the gun then cocks the gun to show he means business. Also, the racking noise that accompanies any sort of firearm, even those without a slide.