Every genre has its own quirks. Romances have to be happy without inflicting instant diabetes. Thrillers must incorporate 'edge of your seat' scenarios. Sci-fi must transport its readers to new worlds with wondrous possibilities and unimagined dangers. Mysteries must have twists and turns.
But how many?
A mystery with no plot twists or red herrings would be a very dull book. Ah look, a crime. Ah look, a solution. Yawn. Readers want to be presented with a puzzle, readers want to have to work at it in order to be able to figure it out. However, a plot can become too confusing because if every page brings a new wrinkle you can end up with a terrible mess.
I try to aim for 'controlled chaos'.
Number: Allowing room in your plot for multiple motives can easily increase the number of twists in the plot line. Multiple motives means a larger number of characters which will enrich the colour and texture of the plot. Red herrings are great, especially if your detective is also fooled by one or two.
Presentation: I try to mix up how the true clues arrive. Some are in conversation. Some are physical. Some are in the make-up of the character's personality. I want my reader to have to pay attention, but I want them to have fun too. I try to remember we read mysteries (and many other genres) for enjoyment. It's not supposed to feel like a school assignment.
Size: There are big twists and little twists. Someone lying about their whereabouts is usually a small twist. Identical twins taking each other's place is a big one. I try to have a nice mix, but I rely more on the small twists. Too many big ones tend to make the plot fantastical and I try for a certain level of reality.
Placement: This is also important. Most mysteries will have their twists in the middle, with perhaps a large humdinger very close to the end. I'm wary of the big humdinger mainly because I don't like reading novels where new information is thrown at me when the end of the book is countable pages away. My thought is always "How did this detective know this when there hasn't even been the slightest hint?" Unless he/she is psychic, I have a problem.
Twists and turns. We'd be nowhere without them. But watch them carefully; they tend to breed.