Want to know a secret. I make it all up. Nearly every bit of my D&D game, I improvise.
I have idea and plans, but when I sit down at the table, ninety percent of what goes on is created on the spot. There are multiple reasons for why this is the case. Often, my players head off in directions that I never imagined. Other times, I get to the table and realize that what I created and built, just isn’t going to work. Occasionally, I just don’t have anything ready; I have good intentions, but like the Road to Hell, I get paved with them. Sometimes, I just want the thrill of creating on the fly. Sometimes, it makes me feel like I am a huckster selling snake-oil.
Now, in my defense, I do create NPCs, and towns, and monsters with which the PCs may interact. I love making and twisting maps and often have those on hand to help orient the PCs. I design cultural touchstones, so the Storm Kingdom is different than Neverwinter. I have been making secret cards for the NPCs and special places and items that exist on Rilmorn. I craft magic items, sometimes before the game and sometimes during the game. I plan combat and social encounters to challenge my players. Yet, despite doing that work, I still seem to be making things up at the table.
There’s my secret.