Today I'm making up for being late with the post last week with a bonus post. I'm going to describe how I determine how much to prep. I prep a lot for my games. That's just my style, but I think it's important to do at least a bit; as others have written, your prep should be efficient. It's all about the most bang for your buck, so to speak.
I write two steps ahead of my players. Being two steps ahead of the players is very important. Two steps exactly. Here’s why…
While you’re planning, the PCs are currently in transition. They have finished something (last encounter; last session; last adventure) and are about to start something else (next encounter; next session; next adventure). After the next thing is where you get two steps ahead.
Your next step needs to be informed by where you are, and where you want to go (two steps ahead). To build the hooks into the next step that lead to the step after, you need to fully think through two steps ahead to generate them. You're on A. You're planning B. You need to know quite a lot about C before you can plan the parts of B that lead to C. You're close enough to C to start committing to certain things, and not so far that you really risk wasting that effort if the PCs go a different way.
Planning further than two steps can be harmful. When you set things in stone, you’re loathe to change them; and even if you maintain your flexibility, it can be a waste of time as you’re constantly rewriting. You might have the time for that, but I don’t.
What about outlining the campaign?
There are two kinds of campaign prep I do: Scene Daydreaming and Adversary Planning. Scene Daydreaming is when I come up with a really cool scene I want to see happen. I don’t actually write a set of rails to get the PCs there; instead I look for opportunities to use that scene whenever I start adventure and session planning. Adversary Planning is where I come up with cool bad guys and what they want and are trying to do. I don’t build rails around this either. Usually I don’t care if it ever comes to light – it just helps me design my two steps.
Isn’t the next adventure more than two steps ahead, in terms of scenes?
You might notice that I’m staying two steps ahead on multiple levels: Two scenes ahead, two sessions ahead, and two adventures ahead.
My scenes have three stages of writing: Outline level, stats level, and story level. At the outline level, I have a few sentences about the scene, what it could be used for, alternatives to it, and how it connects to the plots in the game. At the stats level, I have provided stuff like maps, handouts, skill check target numbers or modifiers, and NPC stats (as needed), and I may have written some “box text” or bullet point notes. That scene is still not set in stone! I change my scenes on the fly as they approach, based on the characters’ actions. At the story level, I determine the reason why the scene is happening, and what ripples it will cause. That sets the scene’s contribution to the story that’s unfolding.
What about modules?
I actually run a lot of modules these days. I add a lot of detail to the modules, including new encounters and weaving in character plots and hooks. Even a heavily designed module encounter is only "stats level" design - I still have to tailor it to the player characters' decisions and recent actions. Have they summarily executed all the other goblins? Well then this next room's goblins will express disgust at the PCs' murderous slaughter, yet also be afraid for their lives; and they might try to flee but they will be unwilling to surrender under any circumstances. Without responding to player actions like this every now and then (you don't have to do it for every encounter), the module comes across as canned (which it is, but you don't want it to feel that way).
What modules give me is a lot of "stats level" work, some of which I have to reject, rewrite, or add to. I find that I prep almost as much for modules as for home-brewed adventures. But I get more "bang for my buck" because most of my outline and stats level prep is done for me -- assuming the module is any good.
You know I love examples!
Here's my example. The PCs will be investigating a shadowy temple that they discovered last session.
Outline: Written as part of adventure planning.
Shadowy temple, PCs might investigate – may be spied on by cultists who have abandoned the site since it was discovered, may discover specific things have been moved out (so that they can search for them later).
If I did some Scene Daydreaming and had a cool idea about chasing down a spy who made the PCs in a crumbling district full of slums and old ruins, then this is where I deposit that scene. If I did some Adversary Planning about a cultist spy who murders witnesses and shadows the PCs, keeping tabs on their moves, this is where I insert that guy.
Stats: Written as part of session planning.
At this point, I will draw a map of the temple, find the stats (and name and description) of a spy and set the roll required for the PCs to notice him; determine what the spy knows and what system I will use if they try to extract that information; google pictures of things that work for the missing items that they may look for elsewhere as clues; and so forth.
Even if I do a lot of Adversary Planning, I don't actually stat out my adversaries until I'm a few sessions from using them. The reason is that I need a good idea of what the PCs' current skill levels are and what the circumstances they meet the adversary are. These change! In this case, the PCs will meet a potential adversary while he is alone, but the PCs are also unprepared and on the adversary's turf. But it could very well have been a scene where the PCs were prepared; or had allies; or where the adversary had allies; or dozens of XP or a few levels earlier or later depending on the game system...
Story: Customized by the GM two scenes ahead of time.
The PCs have decided to go to their contact, who tells them that he’s heard of some activity over at the old temple site. But next they have to make their appointment with the Duke’s seneschal, so some time will pass. I'll make sure to describe the area around the temple, on the hopes that I can set up a frenzied foot chase through the area and my players will remember the terrain and use it in their action descriptions. Near the old cult temple, there should also be an NPC resident who witnessed people leaving the temple just before dawn – maybe the NPC is someone who just moved into the area and doesn’t know enough to be scared. The resident can describe the objects they took, and give a description of one of them (the spy who stayed behind to see who showed up). This resident will get killed later for informing if the PCs don’t notice the spy. If they do notice the spy, attacking the spy and killing him will have other consequences. Capturing and imprisoning the cult spy will lead to a jail cell murder of the spy and more clues, or perhaps I can make the spy an important cultist who engineers a jailbreak from the inside.
Notice how much more detail gets added as the scene gets closer. How I describe the scene's setting is determined by a combination of prior long-term planning and the player characters' actions just a few scenes ahead of time. The hooks into and from previous scenes are inserted; timelines are solidified; and other incidental NPCs get inserted based on player decisions only a few scenes ahead. My Scene Daydream had a slum, ruins, and a high stakes foot chase; so naturally my final scene plan is focused on making my daydream a reality -- but it's still not set in stone. The PCs might not notice the spy or might decide it's a trap and let him go; or even capture him before he flees.