Do you have any advice for someone about to dm for the first time? I'm less worried about running the session than how the hell do you plan one?
Btw Iove your art and it's inspired me to try out line work again
Thanks! And hey, that's a good question.
Here's the thing I've learned as a DM - you don't have to plan EVERYTHING.
In fact, the less you plan, the more prepared you'll be!*
How I like to think of when I DM is that me and my players sit in the middle of a WHEEL of possibilities. It looks something like this:
Every session you start with, you have a set amount of possible go-to points. These are limited. Usually, your party won't go from sipping drinks at a tavern to walking out the door and fighting cult members in ONE session.
The possibilities are endless, so what you need to prepare is just the next few steps. In the above image, what I mean is that they first two darker shades are representative of what you need to have prepared immediately, and the lighter shades are plans you can have on the back burner, but don't need to flesh out.
As your party makes choices and travels outside of the Starting Spot, you can prepare the NEXT steps based on the ones they chose.
So, say your party is in your tavern, and they decide to go to the Adventuring Guild to look for a job. You don't HAVE to prepare the Heist Mission in the Wizard's tower for that - you can know it's a possibility, but once they've made their first choice, you have a direction.
You can then kind of visualize what their next steps are.
Of course, this wheel isn't one way! Your players could always just... hop over to an adjacent topic! If they're solving a mystery, that could link up to a Cult involvement. And from there, they can discover a Secret Hideout for the Cult, which you already know was a possibility if they were to go into the forest.
And once that sort of adventure has started, you can go ahead and think about what other things you had planned out might link up to or evolve from where they are.
At that point, it's like playing a giant board-game. Which involves laying down track in front of an oncoming train.
My recommendation is that you keep a few things on hand which can be used anywhere:
a few maps that somewhat relate to multiple things on your map (for example, a dungeon-looking map that could be a Secret Hideout OR the Wizard's tower)
Some named NPCs - at least one per location that you can throw up immediately when they arrive
a few puzzles/plotpoints which can act as a placeholder while you think of details (for example, a Mystery can be hard to think of on the spot. Give them some random clues, such as a missing person, a few discarded items, etc and then take your time before the next session to link those items together!)
The rest is.. well... just making it up as you go along!
Of course, that's just MY personal way of doing things. Some people prepare way less, and some prepare way more. It's just all up to how quickly your players move/how comfortable you are with details.