“Is this going to be fun?” is the most important litmus test for anything you run at a LARP.
Your plot, encounter, or NPC may be pretty epic and cool in your head, but it’s possible that you are ignoring how players will experience it.
Keep in mind that players come to the game with a spectrum of motivations. Some love story, some love overcoming challenges, some love treasure, some just love being in their character’s headspace. As such, your content needs to include rewards for numerous play styles.
For example, you may be writing an encounter in which the players finally meet the NPC they’ve been looking for, and he imparts a wealth of knowledge onto them. In the script, you’ve blocked out two hours for roleplay with this NPC.
In practice, a few of the players will want to interact with the NPC, and the rest will probably hang out and wait for something more their speed. Is this two hour long dialogue going to be any fun for them? But if wandering monsters attack the area while the dialogue is going on, you’ve introduced a tactical element to the encounter which will entertain those seeking more visceral rewards.
If your encounter isn’t fun, it doesn’t matter that your plot is engaging, the monsters are well costumed, or that the rewards are glorious. The players will react with boredom or frustration.
Too much of any one thing is not fun. A weekend packed with mindless battles can be as boring as a weekend with no battles at all. Being kidnapped, stricken by disease, or trapped somewhere can rapidly become monotonous. If your script includes the words “the players do X for Y hours”, go back to the drawing board.
LARP is both a form of gaming and theater. As such, it’s about experiencing something (as opposed to hearing a narration about it). Focus your efforts on making the players’ experience as fun, memorable, and interesting as possible. The best way to do this is to hold each plotline under a magnifying glass to see how fun its parts are.