One thing I've found infinitely useful when prepping RPG material is to make problems open-ended. If you read a lot of modules, like I do, you'll end up reading a lot of text going into the rules and mechanics of a situation and also the acceptable solutions.
When you're writing a book or PDF, it's useful to provide examples of solutions to problems. If the players attempt that solution, then great, you have resources there. Or it gives you the ability to provide hints if players need a nudge. But you can't provide EVERY solution. Maybe you run scenarios for sample groups and incorporate some fun ideas the groups had (if you have time). But mostly you'll just provide like the first and second most likely ways to approach a problem and that's it.
If you've played tabletop RPGs, however, you instantly know that NO plan survives contact with the players. That's one of the things that makes DMing engaging. You're always thinking on the spot because of their shenanigans!
So, because of this, if you're writing your own material for your own party, you don't actually need to write down solutions. You can let the players provide the solutions on their own. It saves you mental energy and time as a DM and it removes the shackles of "there is only one solution" that can plague some modules.
Also, as a sidebar, I'd just like to note that a lot of non-WOTC adventures include language reminding the DM to allow players to come up with creative solutions to problems presented in the module. I wish WOTC adventures included stuff like that! It's always assumed to be allowed, but having it written gives new DMs permission to loosen up a bit.
