We all have the illusion that the more we prepare for an encounter the better it will be. But as DMs, we can’t control encounters. We can only prepare to improvise during an encounter. And the more we prepare the encounter itself, the harder it gets to improvise it at the table.
Each detail you’ll lovingly add to your encounter...
“At midnight, Ghibli will sneak up on the PCs when they leave the Inn. He'll steal the key by pickpocketing them when they pass the butcher.” Is a lot harder to pull off than “One of the lord’s evil henchmen tries to rob the players of the key.”
It’s hard to say how detailed an encounter can be before it suffers the bane of over-preparing. Let’s follow the masters of abrevity. A tweet can be 280 characters, which tends to be enough in my experience. An old-style 140 character tweet would be even better.
“A cornfield burnt to the ground. At its center, a hut. Inhabited by a scared, deranged wizard casting fireballs at anything that moves.” - 135 characters
What you still can do to prepare for the encounter
I know, it’s a hard lesson to learn. Or at least it was for me. A few years ago my encounters had a title, an epic (to read out loud to my players), DMNotes (with info for the DM), prerequisites (things that needed to happen before the encounter), and possibly an encounter table with dialog options. And almost all of it was a waste of time. I used to highlight the important parts so I could find and improvise on them while running the game. Turns out I only needed the title and those few highlighted notes. The rest was me improvising. And that’s the scary part. *You can make it easy to improvise but you can't prepare improvisation *. Yet, you will get better at it by playing. And you can not sabotage yourself by not over-preparing.
So be lazy and play a lot of d&d, how hard can it be….