It can be difficult to separate yourself from your own story, so I encourage you to start with a story that isn't yours. For simplicity's sake, I'd also suggest picking a movie. Most tend to follow a formula and that makes it easy to fit the story-line into a few paragraphs. If you can make the plot simple to think about, this makes it that much easier to adjust.
Before we begin, I should mention that this is an EXERCISE, so, for fun and for you to develop your writing chops, not for you to profit from. We don't own the rights to these stories, we are merely using them to build our storyteller strength. Consider yourself doing fanservice to the story. Characters, settings, technology will all remain the same. We are only changing events in an effort to improve the story. Before you begin, take a look around the internet and see what other kind of fan-fiction exists for the movie you've chosen. FanFiction.net is a great place to start. (Still worried about legality? Give Anma Natsu's podcast about the legality of working with existing stories a listen.)
Okay. If you haven't figured it out from the title, the movie I'm doctoring today is Pacific Rim.
Find the synopsis for your movie. Can't find one? Watch it again and write your own. It's important to establish the existing beats of the story before you can go to work on them. I even added a few extra beats to the above linked synopsis from my re-watch.
2. Pilot on the right side of the cockpit controls the right side of the Jager.
3. Pilots inside the Drift speak aloud to each other and separately, even asking each other questions and arguing.
4. Jagers don’t have readings of kaiju signatures.
15. Mako and Raleigh are on separate oxygen supplies.
2. Allowing for some hand-waving science, this is still wrong. The right side of the brain controls the left side of the body.
3. & 13. We were told that the drift is a total melding of minds, so if the pilots speak aloud it should be in unison, and if you and another human being are sharing a mind, there shouldn't be any room for confusion or disagreement.
4. It makes no sense for mission control to be talking the Jagers through the fights. If mission control can read the "Kaiju Signature" (glossing over how that's possible), then the Jagers should have that ability as well.
5. Barring off the entire Pacific would cause serious economic and ecosystem disruption.
6. Only two. Even though there are a million people walking by all the time in the Shatterdome.
7. This should be a no-brainer. The Russian (Cherno Alpha) and Chinese (Crimson Typhoon) teams are there to look awesome and then die. We don't care about their deaths, and neither does anyone else seem to at the Shatterdome. I was mostly upset that I didn't get to see more three-armed fighting as opposed to feeling the loss of five Jager pilots and two Jagers. With two less Jagers, the plan to detonate the Rift should be in more jeopardy, but we don't get any trepidation from the teams or anyone on base.
8. Jagers fight by boxing and ammo, with the occasional melee weapon thrown in.
9. Mako almost killed a ton of technicians on base, would also be causing severe damage to the hanger and other Jagers. Raleigh's memory of his brother's death came back fresh once he stepped into the drift, so that will be upsetting him. And Raleigh couldn't pull Mako out of the rabbit hole, so he could be taking out some of his frustration over that on her as well.
10. Pentecost knew this was a risk and let Mako in the cockpit anyway.
11. Allowing that this was a localized pulse, the Shatterdome is right next to the city. At least the buildings next to the harbor should be knocked offline.
12. That is not how EMP's or nuclear power works. (This is a pdf report from Oak Ridge National Laboratory on HEMP, see the appendix on page 167 for explanation of misconceptions.) The EMP can still cause damage to Gypsy Danger because the Jager has electronic wiring and interfacing throughout. She runs on nuclear power, but that does no good if the power can't travel anywhere in the machine.
14. Obvious sign is obvious.
15. It makes no sense for there to be two separate O2 supplies in the Jager. They have separate lines, so in order for damage to occur on Mako's and not on Raleigh's, the cockpit would have to be breached, and it wasn't. And why don't they have an emergency 5-15 minute supply in their suits? They are fighting at the bottom of the ocean, for crying out loud!
16. This is just laughable.
17. Shouldn't have to because of #15, also this gives Raleigh the finishing blow even though Mako has been the one working so hard for it the entire movie. Raleigh has almost no character development in this movie, so his victory doesn't feel as big.
18. No Kaiju DNA!
1. Given, this is a movie, and it can be harder to weave in backstory than it is in a novel. I think they should have skipped the narration and settled for a series of cut scenes between the news reports with CC's of dates.
2. Switch the pilot sides OR say that the pilot on the right controls the left side of the robot.
3. & 13. Make the pilots speak in unison when in the drift, and if they have to argue, have their voices do it "mentally".
4. Give the Jagers a reading on the Kaiju Signature.
5. Move the wall out farther from the coast, make it semipermiable so that small animals can get through.
6. Give them a few assistants, or maybe just one who's interested in both fields. That would give some more comic relief as they both boss the assistant around.
7. We see the Tang brothers (Crimson Typhoon team) playing basketball in a fleeting glance, but they don't have any spoken lines. After Mako nearly destroys the Shatterdome in their first drift, could have Raleigh go blow off some steam with the brothers in a game of horse. This gives the brothers some opportunities to ham it up and show us their personalities.
The Kaidonofskys (Cherno Alpha) do get to say exciting things similar to "Rodger", "Engage", and then scream in agony as they die. But otherwise they're in the background. Give them a small scene as well to make them seem more like real people.
Thirdly, have a scene where Gypsy and Striker are being fitted for their trip to the rift after Crimson Typhoon and Cherno Alpha go down. Have Chuck Hansen, the son in Striker team pair, come check on how progress is going on re-fitting Striker since the EMP would have blown out all the capacitors. He's all cocky and superior, his usual self. Technicians from Crimson and Cherno have been conscripted to help make the deadline, and one or a few of them remind Chuck that if it wasn't for Pentecost's orders, he'd likely be at the bottom of the bay instead of the other pilots. This makes us feel the death of the other crews more and helps chip away at the arrogance of Chuck so that we believe and can support his sacrifice at the end of the movie.
8. Have them do more MMA style fighting in the trials. Or laser tag!!
9. Have Raleigh chew out Mako for bringing that history into the drift and not giving him a heads up first. Then have them be pissed at another since Raleigh screwed up also.
10. Have Raleigh chew out Pentecost for letting Mako in the drift with him and not giving him fair warning. Then Pentecost can still do the "1. Do not ever touch me again. 2. Do not ever touch me again," bit.
11, 12, & 14. Shrink the EMP so that only Striker Eureka is affected. The "fact" that Gypsy is "analog" and shouldn't be affected by the EMP is kind of pointless (besides out and out wrong, hence the use of quotes), since Gypsy Danger goes and pulls the EMP producing organ off of the Kaiju first thing and it only ever got to deploy the one pulse. The Shatterdome can stay up and functional since they pretty much have a sportscaster function in the fights and just give us a play by play.
Raleigh and Mako are deployed to protect the city and have to overcome their differences to initiate the mental handshake. Can have the mental handshake be shaky at first, but then hold firm when the pilots accept their own emotions and the emotions of each other. This gives us more character development for Raleigh who is mopey at the beginning of the story and then kind of on a "I'll just go with the flow" plateau afterwards.
15 & 17. Have both of their O2 supplies be damaged, that way it serves the "ticking time bomb" function but they both have something to . They can set the manual self-destruct together and have a "for my brother," "for my family," "for Pentecost," "for the world," cheesy moment. Only probably more epic and less cheesy. Escape pods can deploy at the same time.
16. Eliminate and just have the Shatterdome have nothing until they see the rift collapsing, then they have to sit on their hands to find out if the pilots make it out okay.
18. The rift reads anything passing through from our world to the other side to make sure that only Kaiju can go through, so it would make sense to work both ways. Have the pilots be unsure if their pods will go back through, but have there be enough Kaiju blood/bodily fluids on the outside of Gypsy Danger that the pods have some on them and can pass through as well, but we (audience) don't find out until the last second when the pods make it through. I would also put the rift on the ground in the "anteverse".