Session preparation can be a big deal for GMs. I specifically started running a D&D 5e game, way back when, not only because I wanted to try 5e out, but because I knew D&D would make me work on my session prep skills which had gotten somewhat lax. For the most part it was working well, but then I read Sly Flourish's The Lazy DM, and the core idea there caught me off guard but intrigued me all the same.
The core idea behind The Lazy DM is two fold: 1) most DMs/GMs spend too much time on session prep doing unnecessary things. 2) You'll run a better session if you prepare less.
Today, I want to talk about this.
Less, Not Nothing
First, I want to be clear - and Sly himself clarifies this in the beginning of Return of the Lazy DM, but the idea is to prepare less not to prepare nothing. You need something prepared to run a session, but most DMs - myself included - will spend a lot of time preparing things that maybe don't need so much preparation time, or any preparation time at all. Instead, the book encourages you to really hone down your prep so that you are preparing only things that your session needs.
The Dangers of Preparation
One of the arguments made against focused preparation is that time spent preparing something is investment. If you spend 2-3 hours preparing a custom monster, a special encounter, or a particular scene, you're invested in that scene. So what happens when your players are trying to find a way to skip it? Yeah, now that thing you sunk an evening into is going to be useless. Objectively you could use it again later or in some other game - maybe. Odds are though, you're going to want to make that thing happen.
This message hit home to me in particular. Recently my players almost skipped an encounter I had worked hard on and was looking forward to. When the players started laying out their plans my heart sunk. What would I do if they skipped it? Not only was it a cool encounter that wouldn't happen, it was an encounter that was meant to take up a good chunk of the session. Sure, I could wing something to keep things going, but improving wouldn't feel as good and polished as planned and the whole point of the D&D game was to work on preparation not improv.
Fortunately for me the players did end up in the encounter without me forcing it, and it was fun, but that being in mind when I read Sly Flourish's words definitely made the point hit home.
Limited Time Needs Efficient Prep
This past week has been particularly busy for me at work, and I was lax at home because of that which meant I found myself Thursday night realizing I hadn't prepped well for the D&D game on Friday. Fortunately, there was a solution. Namely, efficient prep.
With the guidelines from the Lazy DM, and my own thoughts, I focused on 6 things. First, I figured out what the three most important NPCs to the current adventure were going to do. Second, with those 3 things in mind, I tried to plan 3 ways the session could go. And that's it.
Character Driven Makes Things Fun
With my first three things, and five PCs for that session, everything that happened at the table was going to be character driven. Either the PCs were going to have a plan to do something that would take over the session - in which case, I already knew what the big NPCs were doing so I would just have to see how the PC plans and NPCs plans clashed. Alternatively, the PCs would latch onto one or more of the NPC plans and that would be the focus for the session.
Either way though, there was going to be characters - not events - driving the action that happened and that was where my focus was. It worked great, and while the PCs had some things they wanted to do, the NPCs also got to move on their own plans and everything was seeded into the world. Next session I can focus on the same things for world progression, but the PCs also have a concentrated plan for what they want to do, and I can prepare around that easily enough.
Less Prep = Less Investment
The flip side to the danger of preparation is that, in a good way, having less prepared in detail means you are less likely to care if it gets skipped. Yeah, it'd be cool if the PCs ran into the encounter with the King, but it's not like you sank a lot of time into it so if they skip it, it's fine. Which in turn means you won't force it, and the players can impact what happens without having to worry about wasting work.
How Much Depends On You, And The Session
Remember, the idea here is to prepare only what you need. How much you need as an individual is likely different from how much prep I need. You'll need to find your balance point. I'm looking for mine. Also, some sessions will need more prep than others. Custom monsters mean investment and 90% of the time you probably don't need them. 10% of the time though, they can make your session that much more special - especially for a big set piece the PCs are running to. Just don't make that step until you know it's what the PCs are going for.
Let the characters drive things. Your PCs should get first shot, but your NPCs should be ready to push too. Have fun with it, and don't get hung up on details you don't need.
Oh, and if you care to, read the Lazy DM. I don't agree with everything in it, but a different point of view and solid advice is totally worth the $5-$6 he charges.