I've been reading a lot of requested fulls lately. Most requested fulls have pretty good writing. The most common problem is pacing; the second is the lack of twists/turns or surprises in the plot.
A good plot will have at least three twists or turns or places that surprise the reader. As I read, when I come to one of those points, I often stop reading to enjoy the moment. "I didn't see that coming!" and "Yowza! Yikes! Zounds!" are what you'd hear if you were in the room. Cackling with delight, really.
Absent those kinds of twists and turns a manuscript can be perfectly fine, publishable even. But it won't be that super special book that gets people talking. "Oh my god, you have to read this!" kind of accolade.
Those three cackle books are what I'm looking for, diligently!
So, how do you get twists and turns in your book?
I don't think there's one best answer.
I do know that the very best authors do it, and reading them to see how and when is a good idea.
One place to start: Sacred by Dennis Lehane (*SPOILERS HERE*)
The "Mormon" crowd on the green don't try to proselytize Kenzie and Manny. Instead, they're afraid of Manny.
Lehane gets Manny on to the street in a nifty twist too: Kenzie walks in to "the wrong office", but of course it's not the wrong office at all, it's the one Kenzie intends to burgle later (but the reader does not know that when the scene unfolds.)
And then, on page 204, Lehane turns the book around completely.
But twists don't have to and should not all be big ones. Twists and surprises need to be in smaller moments as well, the moments that keep readers engaged and not wanting to skip ahead. If the twists just keep getting bigger, you'll end up with a crazypants soap opera (oh my god, Erica Kane hasn't just been married 100 times, she's a VAMPIRE and a MAN!)
Sunburn by Laura Lippman;
The Word is Murder by Anthony Horowitz;
Before the Fall by Noah Hawley;
The Breach series by Patrick Lee (which surprises me EVERY time...even now.)
Read those with your writer notebook at hand. Write down the scenes with twists (and page numbers so you can go back and find them later--something I'm frequently kicking myself for failing to do.) Study how the writer subtly steers you and your expectations. In the hands of a master craftsman, thinking "oh I see what's coming" is often the first sign you do NOT know what's coming!