At some point early in the 'pre-production'* phase of the campaign, I put together a 'view binder' to serve as a Campaign Book, also known as a Campaign Guide, or Campaign Bible. These serve the same purposes as Writing Bibles for screenwriters (which is where I got the idea). I use each campaigns Campaign Guide to store character sheets, notes, images, maps (see below), rules, and charts, campaign background material such as a timeline, and other bits I know I will need, or want, to reference again, and again.
With many of my campaigns over the years, at the end of each session I collect the PCs character sheets, and store them in the book as well. That way no one can show up to the game, and say they left their sheet home. If the GM is there (me), your character is there. This is also helpful if someone can't make it. I still have their stats, skills, and information if I have to use them in an NPC capacity.
With my more ambitious campaigns, I give each of the players a folder, or smaller binder, to hold copies of many of the pages contained within the Campaign Guide. Each session, or every few sessions, the Campaign Guide gets updated, and so do the players' guides. Many of the players guide entries are Player Handouts, and Prop Documents, but others are game universe notes, and mechanics the player can look at whenever they wish so that they feel like they know what someone living in the setting would know.
My players always love this. It gives them a real sense of investment in the campaign. They usually take really good care of their books, and look forward to updating them. Some will even take their own notes, and/or drawings and put them in their book as well.
Now, I'm sure many people out there do this. This is not some groundbreaking concept. It is useful, and effective, but I didn't turn lead into gold with this idea.
However, my book might be a little different from yours...
A key element is there that there is a lot of art, and very little text by comparison. Not none, but I would much rather show you than tell you in some respects. For example, my Traveller, Star Trek, and Star Wars games usually have several pages of Uniform Recognition, so the PCs know how different personnel in the various government and military agencies dress. Later, when I describe an officer coming toward them, the players will say, "Ah, Imperial Navy, huh? I check his shoulder patch. What fleet is she with?"
The end result is a book similar to the DK Visual Dictionaries and guides.
Images of one of my largest and most complete campaign guides.
The 'Series Bible' for Star Trek: OUTBOUND.
What I don't do is fill it with lots of writing no one will ever see. There are no paragraphs of flavor text, room descriptions, or long, multi-page write-ups of the current political atmosphere in the campaign region. All that is just wasted paper. It does nothing for me. It does nothing to enhance my players' gaming experience.
Maps are also minimal. While I love maps, and indeed see maps as art, I find them extremely hard to use in games. I will make maps of large regions, such as a country, a world, or a sector of space, but the closer one pulls the camera in, the less likely I am to make a map for that area. I'd much rather sketch something out on scrap paper, or a dry erase mat if ones available.
My campaigns nearly always feature the ability for the PC group to move around. Be it via riding animal and cart, ground vehicle, spacecraft, or their own power (flight, super-speed), my players' PCs travel a lot. Combine this with my very open world, sandbox style campaign design, and making maps for a given city, town, or (bleh) dungeon just isn't sensible.
Let's say for example that the PC party begins in the town of Flaire, which lies on the Eastern Coast of Northern Loreia, looking out upon the Northern Atlantean Ocean.
Images from my D&D AD Campaign Guide
detailing my milieu of Aerth.
What should I prepare for them this session beyond these maps?
Do they need a map of Flaire? What if they don't stay long? I suppose it couldn't hurt to make one. Unless...What if they go Southwest to the tri-throned, Dwarven city of Thoel? Rumors abound that the Dwarves there have been making numerous expeditions to the far North. Hmmm. Maybe the PCs will beat them to whatever they are seeking by seeing if anyone in Nouveau Lutetia knows what's going on. So I need a map of Nouveau Lutetia, and everywhere in between that city and Flaire.
Of course, there is always travelling to the bustling city of Rae-Uhn. Aside from seeing the 'Great Golems' there, it will be much easier to find a job, and pick up information in such a busy, cosmopolitan place. So a map of Rae-Uhn is needed.
Still, there is always chartering a boat, or a ship, and traveling across the North Atlantea. I mean, Flaire is a port town, the largest, and most popular on the East Coast. So...let's see...I need individual maps for...everywhere. It's Sunday night, and the game is next Saturday.
It is for this same reason I don't really create flavor text in the sense of pre-written blurbs about where the PCs are, and what they see. I do create writes ups of towns, or planets, and the like, but I keep the info to necessary crib notes. I just need the overview, the details that anyone going there would be curious to know. This gives me a sense of the place, a sense I can then pass on to the players.
Leighton, in the Flux Subsector of Spica.
Major location in our Traveller - Operation: PALADIN campaign
NPCs you've seen before. They are recorded with only their names, jobs/careers/classes or whatever identifies them easily, key stats (but rarely all stats), key skills, and some notes about who they are (Collects Old Sports Memorabilia, Has a crush on Sollor in Engineering, Refuses to Eat or Drink before First Light).
With this out of the way, I can get to the final phase of my 'All Win Scenario' series, which explains how this all fits together to make adventures happen. I realized that without a handle on how I create, assemble, and store my information, the description that is forth coming would read as if I was just pulling everything out of my butt magically.
I'm pulling almost everything out of my butt. And yes, it is magical.
*The 'pre-production' part of my campaign design approach is when I am just started to put ideas together. Usually, this is before - or up until - I have finalized characters from all the players.