Tension

Tension is where the game is at a crucial moment, and there is much to be gained or lost. Every move matters. This makes for very exciting games, if done correctly.

For there to be tension, there must be risk of loss, or (preferably) of missing out.

Tension can range from zero to "if you don't do the thing in time, you lose."

In my gangster game, if you lose all your health, you are eliminated from the game.

My usual preferred level of tension is moderate. If you don't do the thing in time, you aren't doomed. You have to pivot, and change strategy.

In my farm game, if someone takes your space, you'll likely need to pivot, and use those resources for a new plan. Someone takes the spot where you kill the bandits? Instead grow some extra food, to placate your bandits this round. Someone takes the spot where you make pies? Use the salt to instead buy a salt lick for your animals.
I played a prototype about diving. If you run out of oxygen, you have to take fatigue cubes, and are weaker next round. That's boring and not tense. I told the designer to change it so that you lose everything you gained on this dive if you run out of oxygen. Each turn is then a gamble: do I go deeper, or do I go back to the boat, with my treasures?

Time pressure

Urgency is key. There should be "checkpoints". You're under pressure to do the thing, and do it in time!

I recommend using short timers. End of game goals are good, but end of round goals are better.

Some games make you "feed your people" at the end of the round, or pay some cost, to avoid disaster. The round is a scramble to get enough resources in time.

If it works in your game, you can have competitive goals, where the time pressure is that another player may do the thing first. This probably requires hidden information though, or the game will become very thinky all of a sudden, as players must analyse other players' progress towards goals. I tend to prefer private goals.

In train game Ticket to Ride, you collect cards, in order to build routes between cities. However, in many places, only one player can build a route. Another player could build there before you, at any moment. If that happens, you'll have to take a longer path. This is a high level of tension, which makes for a great game.

Vulnerability

In adversarial games, make the players extremely vulnerable.

Being close to death is actually fun, as strange as it may sound.

In my gangster game, players battle to the death. Originally, players started on ten health points. They'd casually attack each other for a while, reducing each other's health, but it didn't really matter. However, once players got to five health or below, they could die at any time. A cliffhanger battle ensued, as players desperately tried to save their last few points of health.

I changed the rules. Players now start the game on half as much health. You can literally be eliminated after one turn. Choose your move carefully.

That's what I call tension!
In Radlands, the cards are so destructive that you can be half-destroyed in one turn. You must race to deal with the opponent's people immediately, or they'll ruin you.

All or nothing

Avoid offering half reward for half achievement.

In my pirate game, you could return pearls for one point each. This wasn't tense. Later, you could only return three pearls at once, and if you did so, you would win. Much more tense. However, it did feel a bit bad when you took your three pearls, and a player stole one at the last moment. So, I let the player also turn in two pearls, but they just get some points.

Offer the players only one opportunity to do something. If one player does it, it can't be done again that round (or even for multiple rounds).

Make a jackpot — a slowly-increasing pile of something. Jackpots grow in tension.

In Agricola, if no one takes the resources on a space, you add more at the end of the round. Do you take it now, or let it grow a little? It becomes more and more tempting, and eventually someone takes it.
In most worker-placement games, if someone takes what you want, you'll have to wait for the next round, when their worker leaves, so you can take it. I wanted my farming game to have much more tension than other games in its genre. In an earlier version of my farming game, the workers never leave. When someone takes the horse, or the cabbage, no one else can ever get it again.