The problem with that is it can look like it's come out of nowhere, and makes no sense. You need to foreshadow and hint, but in a very subtle way. The best twists are ones where a reader can look back and think, 'Oh yeah, I see!'.
There is a philosophy in some mystery writing that says the reader must have all the information needed to solve the mystery, but given in such a way that it is unlikely he will do so. Ellery Queen tended to emphasize this. The reader does not feel cheated when the MC puts it together. They feel the AHA! moment. They do feel cheated if the information was not there - deus ex machine.
Depends totally on the twist, how you handle it. But you can't have something come out of nowhere or you'll frustrate your reader - it's like having an action book in which a never-before-seen-weapon or talent magically appears so the hero can save the day- you wouldn't accept that , anymore than you would accept a twist with no lead up to involve the reader. Think of the story where two guys rob a bank , escape on snow mobiles to their hideout in the woods. Then discover they can't leave because a snow storm has packed them in - with no wood to keep them warm, their only choices are burn the money or freeze. Though, the twist seems to come out of no-where, word choice - stating the men planned everything perfectly will alert an astute reader (nobodies perfect - they've forgotten to stock wood)- as well as setting - not just snow, but a snow storm, puts pressure on their actions. The ironic ending becomes plausible. There was a twist on this theme in a 1998 movie.
Peach, I agree with your idea but don't like the example - a suitcase of money would not provide enough heat to make a difference.
This, pretty much. Foreshadowing is the way to go. If you just put a random plot twist in the story, the reader will be left scratching their head, which isn't the reaction you were going for. You want them to be surprised, not confused. Foreshadowing to future events is the easiest way of going about this, because it plants those seeds in the reader's head.
What everyone else said. Foreshadow. If you do it subtly, drop a hint here, a hint there, an out of place detail that becomes important later, you can weave the whole thing together so that when the twist finally hits, the reader will say "Dang! How did i not see this coming!" It takes practice tho, and i have not mastered it yet, only seen other people do it.
If you have to "pull off" a reversal, you should throw it away. If it's an organic part of the story from the outset, it will be as inevitable as the tide, but may not be obvious because of everything else that is taking place. A twist is a trick, a stunt, a gimmick. A worthy reversal is integral to the structure of the story, not something tacked on to amp up a lackluster tale.
Lovecraft had some good "twist in the tail" stories. I think it depends on the kind of story you write though. But, if memory serves, aren't such stories bound more on word count, too? I don't think I have come across one of these stories that exceeds a 2k word count. I may be wrong, and I may be looking at all the wrong material, but that's just what I found.