Game prep is the thing all GMs fear to some degree or another. Whether it’s fear of not having enough time for prep or having no ideas for prep, that fear doesn’t go away as your GMing skills increase it just lessens. There are probably hundreds or even thousands of ways to game prep – many unique from person to person – but here’s mine:
The first stage of game prep for me is essentially daydreaming. I let my mind wander, watch TV, play video games, read books. This step is highly important. I can usually find what I need for my game by not looking for it. This is usually done a day or two before I start actual prep, but if I need to brainstorm a bigger plot it can be a week or even a month of just vegging on the topic.
Next, I take my idea(s) and line them up with the campaign setting, the player characters, and the things that have come before in the game. This is usually the hardest part – as a campaign progresses it accrues more and more things that the GM needs to remember when he wants to add more to it. A good foundation helps with that, but no matter how you cut it eventually you’re going to keep good notes. (I’ve talked about that before here.)
Once I’ve put some thought into what I plan to do I write it all down. That’s note to say I make detailed pages upon pages of notes. In fact, because I work better when I’m improvising I tend to make session notes as bulleted points. “Sam gets attacked and possibly stabbed” is more my speed than a page-long spiel about how the player character Sam might be stabbed after they are attacked, what sort of attacks Sam’s foe might use, and so on.
Once I’ve gone over the (obvious) implications and made notes of what I want to do the next thing to do is internalize it. I start by remembering the the current campaign canon and looking over my prep notes as well as the notes from previous game sessions. A campaign wiki is extremely useful for this.
In Action Stage
Once I’ve internalized my plans it’s time to do what most would consider game prep: writing up NPCs, setting up maps on VTTs, etc. Once I have what I’m doing firmly in mind this stage is the easiest and I typically finish within a day. Sometimes I need help from my more image editor competent players, but usually I try to work with what I have in my VTT resources bin.
Picking Over the Bones
Those are the five major things I do. I’m sure I’m missing little things in between and each campaign has other steps in between – for example, in AEON (my supers campaign) I need to build the powers out according to the specifications of the campaign otherwise things get wonky. There is more leeway in games like DF and MH because sometimes things just work that way – you don’t need to “show your work.”