Plot Twist! Or is it...?
Plot twists have a tendency to be misinterpreted by new writers. Even though I am a new writer myself, I recently got schooled on the subject and it changed the way I approached the subject. I saw a post on Reddit that was along the lines of "so I have this story and I want to add a plot twist but I don't know how". I'm of course paraphrasing, and while I understand the spirit of the request, it's the wrong way to think about it. First of all, "I want to add a plot twist" is the easiest way to jump the shark in your story. If you find that you have a desire to add a plot twist, then you are artificially shoehorning one into your story. This will hurt your story more than help it. Why do you need a plot twist? And why do you need one right now? Are you, as the writer, just getting bored? Then that's a different problem. This artificial desire to have a plot twist also leads down a slippery slope and what may start out as a slight twist becomes a completely implausible, random thing that takes your reader out of the story.
Secondly, plot twists, the way new writers tend to think of them, don't happen in real life or in good stories. The best way, I find, to think about a plot twist is to ask "what is a surprising, yet inevitable thing that can happen right now?" The surprise element is what makes it a plot twist, but the inevitable part anchors the twist to the reality of your story so that it doesn't seem random or implausible. Don't think of it as adding a plot twist TO your story. Instead, think of it as pulling a plot twist FROM your story.
There are several ways you can pull from your existing material to create a surprising yet inevitable twist. One way is by giving your characters incomplete information. If your characters don't have all the puzzle pieces, then there is a natural hole to exploit. You typically see this done in detective, or mystery novels. It's a clue that Sherlock Holmes missed the first time around. It's a misinterpretation that Robert Langdon makes in The DaVinci Code.
Another way is simply by asking "what is the worst logical thing that could happen to my characters right now". If your story involves people hunting wolves, then the worst logical thing could be that they've accidentally wandered into a wolves den and are now surrounded. If your character is divorced, maybe they get matched to their ex on a blind date. You might want to argue that illogical and random things do just happen sometimes. A man walks down the street and gets hit by a car. Is that random? Cars drive down streets. People walk down streets. What made the driver hit him? He was busy texting? Not random. He spilled coffee on himself and lost control? Not random. The car slipped off the back of a tow truck? Not random. It was probably poorly secured, or the cables were frayed, or the chains were rusty and weak. If you really peel back the onion of "random" occurrences, you'll find that they're not random, but rather just a series of causes and effects that are logical in the world.
You can also make plot twists feel less random by subtly foreshadowing throughout your story. These should be clues that on a first reading stand out just enough to make the reader wonder, but move on. Do this two or three times so that the feeling of mystery grows and increases the payoff when the plot twist happens. Be careful not to shadow too many times, or you risk the promise of the plot twist becoming greater than the plot twist itself.
All this is to say that the best plot twists are organic and should make the reader feel like "oh man I should have known! I should have seen that coming" and when they go back and read it again, they can see all the clues that pointed to the plot twist. You should never make your reader feel like "what? that came out of nowhere."