- Mutual Hunt (as Zak describes): Find how to kill Freddy Kreuger before he kills you.
- Escape: Find the way out of Westworld before the robot gunslinger finds you.
- Protection/Rescue: Find Dracula before he turns your girlfriend into a vampire.
- Justice/Vengeance: Find and stop Jack the Ripper before he kills again.
The last two, of course, depend on the PCs caring about whatever it is the antagonist is going to harm or steal. Many fantasy/sci-fi stories (and D&D scenarios) use a cop-out and make the final result "the end of the world" and thus indirectly the protagonist/PCs, to force everyone involved to care about the stakes. However, a better solution is to just postpone those kinds of stories until the characters have grown a bit and acquired "stuff" to care about. For one-shots or new campaigns, escapes and mutual hunts work better.
Now, my main reason for writing this post wasn't to break down all the variations on this idea, but to point out that it works great for improvised mystery (InSpectres) as well. In InSpectres, your job as GM is to come up with an opening scenario (the characters are here, this stuff happens) and a few possible explanations for what it all means, but nothing is set in stone; what the players do determines what the solution to the mystery actually is. For example, when I ran the Lovecraftian variant (UnSpeakable) at a con, my idea was to do a Lovecraft/Supernatural (TV series) crossover set in the '20s. I started the PCs as random customers at a roadside diner who see a car roaring past; there's a woman struggling to get out of the car and a creepy-looking driver. I had a historically-accurate road map and some ideas of what might be in different locations.
The players, as completely new players sometimes do, ignored the bait and just kept sitting and eating.
I didn't have formal guidelines like Zak's, but instinctively I knew that if the PCs refuse to go towards the adventure, the adventure should come to the PCs. I had an identical car with identical driver and female victim roar by. And another. And another, and so on, shifting the focus from "should we rescue the girl?" to "why are there all these creepy duplicates driving by?" The PCs go outside, other stuff happens there involving hell-hound-ish creatures, there's a brief moment where they barricade themselves inside the diner, they kill the creature, then they head into the wooded area behind the diner to investigate, discovering a stone slab that seals the entrance to a mysterious underground chamber.
None of this was planned. The "map" of the area was just "there's a diner here on the road, and most of the rest of the scenery is the town where I went to high school". All the other details were invented in response to what the players did; when they went to investigate stuff, they found stuff; when they retreated, stuff found them. Standard InSpectres die rolls determined whether these events were good or bad.
The reason why the players enjoyed the game and didn't feel railroaded was because they could change the way events unfolded; even if they didn't know that all the details were improvised, they still knew that they could choose where to go, what to do, and their success was determined by die rolls, not GM fiat.
And, although they may have been lost at the very beginning of the scenario, once things started rolling, they became less lost, even when things looked bad. That's because it felt like a familiar horror-movie pattern, and in fact was a familiar horror-movie pattern. Everyone knows what to do if you get trapped in a diner surrounded by monsters, because they've seen it several times already (figure out a way to kill 'em or distract 'em while you escape, or figure out a way to call for help.)
So the conclusion is: if you need to improvise (whether or not you planned to,) the hunter/hunted pattern works great for investigations.