Someone on Facebook posted a simple question - it seemed simple - "How do you start working on an adventure?". My gut instinct was to say "at the start", but then I thought to myself that I do not always think of it that way. In fact I generally do not think that way...
I realize this is not a complete guide to writing adventure, they are just ways to start thinking about them.
Here are 5 different ways I think of adventures.
1- From a plot In this case, I think of an overall plot. "The guy wants to do something." It is as close to start with the beginning as it gets. Here you have an idea of a plot as a whole.
2- From the characters "What if the Avengers did [...]?" Here you have WHO the PCs are and have to work from there. This is a good way as it often dictates some tropes: villains, type of stories, locations, genre. You would not take superheroes for a very down-to-earth plot, just as you would not use the cast of CSI for a superhero adventure.
3- From the villain Similar to the previous entry, however, here you start with a villain. "What if Magneto decided to [...]" as with the heroes, your villain will provide you with some of the elements of setting.
4- From an encounter Here you think of an encounter - not necessarily a combat - but some type of situation the PCs have to resolve or deal with. "What if you all just woke up without any memories?" This is really interesting because it can be whatever. I will admit that this is one of the most common ways I come up with ideas and plots.
5- From a twist The "M Night Shyamalan"... Here you start with a twist: usually a revelation that changes the rest of the story. The PCs realize that they have been manipulated all along, or they realize that all the NPCs they met so far are ghosts.