The bulk of this post was originally posted to Twitter back in the summer of 2018.
One piece of advice I give both new Game Masters and people looking to publish their fantasy ttrpg adventures is my method of adventure creation. Taken directly from the images above, with a few new additions, it breaks down like so:
1. Start with an event from human history
The 12th to 17th centuries work best but it really doesn't matter. Find something specific that piques your interest. Now imagine it weirder. What if it went differently, or was way bigger? This becomes your premise/setting.
This doesn't need to be a conflict. It can be as simple as a natural disaster, or as benign as a new kind of shop opening for the first time. The main reason to pull from human history is that too often fantasy adventures are inspired by other fantasy fiction and media, which can lead to tired and repetitive ideas.
As always, be mindful of your intended audience.
2. Create an adversary
This character stands in opposition to your players. They are informed by your history and use it their advantage. It created them, or they it. They don't need to be evil, but it helps. The players should want to oppose them. They drive the conflict.
I've found that players tend to remember specific villains and adversaries far more than they do setting details or lore. Give your players a villainous character to latch on to. Whether this character remains a villain through the whole adventure is up to you (or more often, it's up to the actions of the players).
3. Root it in a place
A dungeon, a house, a forest, a town, a city, whatever. A place impacted by your history and dominated/threatened by your adversary. A foreign and new place for players they'll want to explore...and eventually own. This is where the adventure happens.
The more unique the location is, the more it will stand out in your players' memories. Lots of adventures happen in caves, dungeons, and temples. If you want to stand out, set yours in a factory, a museum, an art gallery, a hospital, or a magical laboratory.
4. Make it fantastical
If using D&D, change things up to suit the setting and world. Some say do this step first. I say no. Don't let a system/setting/canon dictate your adventure from the start. It often leads to less original work. Be weird first, then adjust it to fantasy.
If your chosen location or premise doesn't fit the technology or society of medieval fantasy, don't be afraid to change it. Add magic and monsters to it, change it to suit your needs.
This is the step where you can change things the most to suit the sensibilities of your audience and your players. Problematic or objectionable content can be changed.
This is just the tip of the iceberg when it comes to adventure design. While it shouldn't be taken as gospel, it's helped me come up with adventure premises and ideas when I'd otherwise be stuck. I hope it helps you too!