Choosing a Theme
Choose a fascinating theme. When you tell people the theme, they should immediately be interested.
Players and publishers are not interested in "a pirate game" or "a train game". To a jaded publisher, a game about the sewage system is vastly more interesting than another game about zombies. I kid you not. Your theme should be interesting, but doesn't need to be totally zany. Zany is definitely good though, if you can manage it. If a publisher somehow gets around to evaluating a boringly-themed game, and the mechanics interest them, they'll just retheme the game to something else — of their choosing.
Don't make your game literally ten times harder to publish, by choosing a boring theme. It's ludicrous to have complete freedom with the theme, because you're designing theme-first, yet not actually choose an interesting or novel theme.
Even if your theme has been done before, and you don't want to change it, you can still put a new twist on it. If you have to do zombies (which you shouldn't), make it "zombies in Japan" or "zombie cats" or something.
You can just choose an amazing theme with no relation to your mechanics.
I would've made the game about animals, or something with more variety, but Wingspan's bird theme has helped make it hugely successful.
People don't actually want something new. They want to experience something they already know, but in a board game.
You might say that your newfangled and unique world is actually really good, and it will resonate strongly with the players. That's great, but are you actually going to be able to convey it? Players aren't going to read some irrelevant story from the rulebook. All you have is your artwork and names, and they have to convey the theme alone. It's really hard to teach players a whole new lore with just art and card names. They'll just see random names and artwork, and ignore it.
Magic's card sets strongly evoke things you already know — stories, themes, countries, and real history. How about ancient Japan world, with ninjas? How about an Indiana Jones adventure world? How about a world based on children's fairy tales?
Tap into lore the players already know and love.
I'd like to play a game about running an ant colony, or creating a mosaic. I know what those things are, and I want to play them in a game. I'm not so interested in being the Archmage of Kronglor, or recovering the Five Galactic Shards of Kozmog.
People need to be captivated by the theme of your game, and that's only going to happen if they can actually understand it.
I've designed games on all kinds of different themes, and people's reaction was usually fairly muted. Then, I started making a game about kids roaming around a neighbourhood on their skateboards, and getting up to all the mischief that kids get up to. This theme resonated strongly with people, and they were immediately fascinated and engaged by it. If you're designing theme-first, this is what you should be aiming for.
Generic themes
Do something that hasn't been done often, or, better yet, not at all.
Do not do generic fantasy. Fantasy is somewhat relatable, but it's massively overused, and many people already know that they don't like it. I don't want to see dragons and warriors. I don't want to see an elemental overlord with frost power. Create your own fantasy. It won't be relatable, but it might be interesting. I don't use creatures from pre-existing fantasy, or even anything that looks like them. Even better, find a type of fantasy that people know, but that hasn't been done in a board game.
Do not do generic sci-fi. Evoke Bladerunner, Alien, Akira, or something.
My game Radlands was originally a generic futuristic game, but Roxley changed it to an over-the-top Mad Max theme. It was a huge improvement.
Do not use anthropomorphic animals. This cheese has been done a million times, and is overdone lately.
And, when you choose your theme, tie absolutely everything in your game into it.
When and where?
The real world is where you'll get the most relatable stuff. However, the real world is fairly limiting.
My gangster game fits perfectly into the real world. It uses so many real life places, and gangster tropes. It's my most relatable game.
Sci-fi is probably my next choice. It sacrifices some relatability, but isn't limiting.
Early on, there was a suggestion that Radlands could be WW2-themed. But how could I make dozens of clearly-different cards in such a world? The Mad Max post-apocalyptic theme was also suggested, and I enthusiastically endorsed it. This sub-genre of sci-fi does violence and destruction very well, and I could throw in wacky science to handle the rest.
Fantasy works, but is massively overused. Fantasy is also fairly unrelatable, except for its historical component, and all the stuff that's been used forever, like orcs and dragons.
Historical settings are a very restrictive version of the present, and are only occasionally appropriate. You would usually want to start with this theme, and build the game around it.
At the start, leave your theme broad, so it doesn't restrict you. Don't choose the exact time period, location, and size of your theme at the start. As you develop the game, your choice of individual cards and resources will help narrow things down.
Feeling of the theme
I'm not really wanting to just evoke the theme itself. The theme leads to a larger feeling of the theme.
I don't just want a pretty, pirate-themed game. I want to feel like a pirate — roaming the sea, attacking other ships at will.
I don't want a spy-themed game. I want to feel like a spy — planning secret moves, and having secret information.
In case this distinction isn't clear, think about some examples from real life for a moment, without thinking about board games.
Imagine you're a kid arriving at a theme park, and there are more rides and activities than you can imagine.
Imagine the feeling of exploring a haunted house.
Imagine you're at the edge of a vast, unexplored wilderness.
Think of a game you really like. What is the feeling you get when you play it, or that you got when you first played it?
Turning a real-life feeling into an actual game is extraordinarily hard, but you only need a small amount of that feeling to come through in your game, for it to make an amazing board game. This is done not by slapping a theme on your game rules, but by carefully choosing game rules that bring out your theme.
Theme size
The size of the theme should also match the size of the game. Do not try to attach a big story to a small game.
You want the smallest possible theme. Only go bigger as your game content demands it.
Azul is a game about arranging coloured tiles. The theme is that you're making a Spanish tiled floor. That's an appropriate theme.
Codenames is a word association game. It's themed as a game about secret agents. That theme is completely irrelevant to the game.
In a friend's prototype, you place object tiles around cat cards. When a cat is surrounded by objects, you add up the points on the tiles, to see who takes the cat. This game was mechanics-first, other than the very general "cat" theme.
We went through all kinds of big-picture themes for the game. It could be a cat adoption place. But why would you adopt multiple cats, by placing objects around them? I suggested a cat café. That was better. However, nothing else in the game said "café". We agreed in the end that the story was just that you were having fun with cats. You give them objects, and they like you, and come to you. That was the extent of the story. It was the correct choice, because it matches what the game actually is.
I've seen numerous basic number or colour-matching games, with some kind of epic legend as a theme. Don't just pick the most awesome theme you can think of. Find whatever matches your game best.