I often say that editing is as much about what is put in, and what isn't. I focus a lot on reducing visual clutter, but today I'm going to talk about story clutter.
When an editor makes a trailer from a 2 to 50 hours of footage there's a wealth of dialogue to work from. I have my system for sorting dialogue into categories, but I also have a reverse filter that makes me skip over dialogue or trim it during editing.
What are the lines of dialogue to avoid in a trailer?
Moment to Moment Minutiae
These two things either clutter up a trailer's story, or they'll go in one ear and out the other, so they might as well not exist.
For most trailers the character's name is not needed to tell the basic story. The only exception are for stories about established characters like Sherlock Holmes where their name is common knowledge, and part of the message is: "Look, a new Sherlock Holmes story!"
Just think about all the gritty reboots, remakes, and sequels where a HUGE DEAL was made of the character's name being revealed. Sometimes movies get super cheeky, and tease the audience by not saying it right away because the people telling the story know the audience is expecting it.
If the trailer doesn't have this sort of established character, the name is superfluous. Sometimes it's even hard to remember a character's name after hearing it multiple times in a two hour film, so why bother trying to make an audience remember it in a 90-150 second trailer?
Think about Star Wars movies. These are the rare movies where the character names stand out so much both because the history of interesting names in the franchise, and intense fan scrutiny. A lot of us knew Qui-Gon Jinn's name way before The Phantom Menace came out, but his name isn't even said until about an HOUR into the film. And yet, despite the ubiquity of Star Wars character names, you're not going to hear them in the trailer.
If there was a line for Rey, Finn and Kylo Ren where they said their names, what would that tell you about them, and what the story of the character is going to be? Not much at all. Maybe if Kylo Ren was a "Darth" character. Now before you point out where I'm wrong about Star Wars trailers and character names I'll just link it. The teaser trailer for Star Wars: Rogue One starts with Jyn Erso's name. Take a look:
Now imagine if those first lines weren't there. Would you be feel like relevant information was left out? Would you ever think to ask: "But what is her name?" I'm guessing not.
If it doesn't contribute to the story, cut it.
Moment to Moment Minutiae
There's a lot of dialogue in movies and games that has no bearing on the larger plot or lives of the characters. Think of Luke whining to Uncle Ben:
To the larger narrative, this line is only saying Luke is being forced to do something he doesn't want to do. Power converters don't affect the story, and it doesn't matter they're at Tosche Station. There are tons of lines in the Star Wars films that wouldn't make good trailer dialogue because they just small moment to moment details. For example:
Luke bragging about bullseye-ing Womp Rats
Yoda critiquing Luke's terrible tasting rations
C-3PO talking about R2D2 turning the heat on in Leia's Hoth quarters
Lando complaining about labor disputes
When evaluating a bit of dialogue for trailer selects, the question to ask are:
Does this dialogue establish or connect story details?
Does this flesh out a character?
Can this be made clearer when paired with visuals?
You can use these questions to both select or filter out lines. It helps to watch a ton of Hollywood movie trailers. If you want to get in really deep, watch a ton of trailers, and organize the lines into categories. It takes practice to develop an ear for dialogue that will or won't work in a trailer, but after a while it becomes second nature.