How to prep for a DnD session

How much, and what, to prep are contentious questions among DMs, and everyone will have a slightly different approach. Some like to have very minimal prep and improv the majority of the session, some like absolutely everything planned out to the nth degree. I'm somewhere in the middle, but I usually err slightly more towards over-prep than under-prep. In large part, this is a result of how I naturally find myself thinking about the story and the characters between sessions (often at 3 in the morning when I can't sleep) so I come up with new ideas and twists that I then flesh out when I actually come to sit down and write out my prep. Maybe my system won't work for you, that's cool. Take anything you like and leave the rest. There are five main parts to my prep, 4 of which are driven by questions.

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What do I want to happen in this session?

The first step is to think about the overall story arc, and those of my individual players, and how I want to drive the story on in the next session. What information do I want to disclose? Which people they might meet? Which items will assist them in their journeys? Where will this take place? These questions give me a frame of reference to work with, and ensure that the session is going to be relevant to the various ongoing story threads. To me, this is essential, and ensures that I'm running sessions which are going to make sense within the overall campaign, and not just some off the wall thing I want to do because I think 'oh, this monster is cool - I'll make them fight that!'

Once I've thought a little about these questions, I usually have a rough outline of how I'd like the session to go, and the specific prep I need to do becomes clearer. Are they likely to get into a fight in the ruins of an ancient university where they will run into one of the antagonists? Better make a battle map. Are they going to overhear a conversation between the Town Master and the head of a guild looking to blackmail him? Better spend some time thinking about each NPC's motivations, and maybe write down a few prompts to help me when roleplaying that conversation. Whatever tasks come to mind as a result of thinking about the big questions of the overall and individual stories, and how they might develop in the next session. I will then write these specific tasks down in an online to do list and check them off as I finish them.

What NPCs are in the session?

Once I have a rough idea of what I want to happen, that will give me an idea of which NPCs will be in the session. If they're a recurring NPC, this doesn't lead to any additional work, as I'll already have notes about their appearance, background and stats etc saved online. I'll just have to make sure they're easily available (if I foresee combat, for example, I may pre-populate my initiative tracker with their stats). If they're a new NPC though (and if they're somewhat integral to the story/ likely to be around for a while), I'll likely spend a little bit of time thinking about their background, and any specific information I need to have figured out about them. Usually this is pretty straightforward - I'll have likely already thought about how this character ties into the story just as I've been going about my week, so when it comes to writing it down, even just a few sentences of backstory is usually enough.

What's important though, is having at least a basic sense of what the character thinks and feels, any alliances/ relationships that are important to them, and any changes they'd like to make to the world. These questions will help drive your improv with the character later - both making it easier for you in session, and also making the world feel more consistent and believable. Like I say, even a couple of sentences can be enough, but it will make a big difference to your session. After that, I'll also make a note of their stats (which I'll either homebrew, or just grab the stat blocks of an appropriate person/ monster from the Monster Manual(*) - and this can always be tailored on the fly if you drastically over/ under power your character). Once the NPC page is written, I'll save it in my online notebook, and populate their details on the initiative tracker if it's likely to be necessary.

What's in the world?

After I've got a general plan and I know what NPCs are likely to show up in a session, I also have a think about the part of the world they're inhabiting. Thinking about and prepping for these surroundings will be more or less intense depending on where you are, and the type of session you want to run. If my players are approaching a new city, then the prep could be quite intense, as I may have to think about a number of different shops, what they sell, and who the vendor is. Or maybe I want to think about who's at the town hall, or in the jail etc.

If they're going to be spending much of the session in combat though, it may be a lot simpler - perhaps thinking about what items in that location could be used as cover or as weapons in the fight. Or think about what might happen in that location to make the fight more dynamic - if it's at sea you could have waves crashing over the deck, or whirlpools to avoid. If it's in an old castle you might have chandeliers falling, or parts of the building collapsing, or hidden passageways to be discovered etc. Whatever you like. While planning out a city might take serious prep time, thinking about how a single location can make your fight more interesting might only take 5 mins - but it would pay off massively when you have a really intense, exciting combat session.

Think about the unexpected

Once I've got an idea of a rough session plan, the characters that are going to be in it, and how they interact with the world around them, I'll spend a little time (usually only a few minutes) thinking about unexpected ways my players might react to the situation they find themselves in. What if they talk instead of fight? What if they try to bribe the Town Master to get them out of their prison sentence rather than do the fun jail-break session you had planned? What if they want to sit playing dice with the random people in the Tavern instead of meeting the wizard who's offered them a lucrative quest? You don't have to (and shouldn't) spend ages thinking about every possibility - because that takes part of the fun out of things, and you couldn't think of everything anyway. But just taking 5-10 minutes to think about how your players will inevitably try and break your scenario, and maybe having a couple of contingency plans loosely thought through, will make things a lot less scary when it happens in-game and you have to think on your feet a little.

What props might I need?

Usually the last part of my prep is to think about any physical (or digital) props I might need for my session. Do I want to make a battle map or use theatre of the mind? Do I want to use terrain instead? Do I want to give out any custom spell cards? Do I want to make any tokens etc to give out to my players? Effectively, you can spend as much time as you want on this stage - and if you get to the point of making terrain and custom props, this can easily amount to several hundred hours over the course of a campaign. If you have the time and you enjoy it, then go for it. If you don't though, then I'd encourage you to prioritise the other stages of prep over this one. Time spent considering your story and characters has, in my experience, a much bigger pay off than time spent preparing physical props. They are a final flourish to make your sessions extra special - but they shouldn't be created at the expense of actually having a compelling story, interesting characters and plot development. A battle map you sketch in 5 minutes will have 90% of the in-game utility of a custom terrain piece that takes 20 hours to construct. So, I'm definitely not saying don't do this - I love props and being able to physically hand things to my players, but I have a fair amount of time to dedicate to my prep. If you don't, scale back on this stage.

And that's about it. It's difficult to give an accurate estimate of how much time this adds up to on a per session basis. If it's an expansive session, where my players have free reign in a city they've never visited, it may be 3-4 hours of prep for a single session (depending on how many puns I want to sit and make up for homebrew items available in the shops). And while that sounds like a lot, the great thing with keeping all my notes online and searchable means that anything which isn't used can be easily recycled for the next city they visit (or even for my next campaign). If it's a more contained session in just one location, with NPCs who have already been introduced and who I have a good grasp of, then I may literally take just 10-15 minutes planning a combat scenario and the different elements that I can bring out to heighten the tension when necessary. On average, I tend to prep for about an hour or two between sessions - but as you get more experience of it, you'll both get more efficient with it, and you'll gain a better understanding of which things your players really appreciate, and where it's worth spending a bit more time to make something extra special.