When I was in college, I had a roommate who made life extra fun. One day, she came walking in the door with a dart board. She'd walked into one of our friend's apartments during a party and lifted it off the wall without anyone noticing. She put it up front and center in our living room, and said she wanted to see how long it would take them to notice it was gone. If they noticed it was theirs when they came to visit, they could of course have it back.

And so began the Wall-O-Klepto.
It became an enormous practical joke, where we'd sneak things from our friend's places and put them on display. Most people noticed right away and got their stuff back. It took the dartboard guys a little longer.
And then there were the bowling pins. We stole them from a couple guys a few houses down from us, put them on top of the TV...and a few days later, they had been stolen from us. We got a ransom note, followed by several more (including a clever little one that came in the form of one of those "have you seen this person" postcards in the mail).
We were positive it was the guys across the street, and we HAD to get those things back-- after all, they weren't ours. We tried several tactics, including sneaking into their house while they were gone, but never managed to find those pins. And, of course, we refused to give into the ransom. In the end, it turned out that the culprits were actually the guys we'd stolen the pins from in the first place.
It was quite the exciting and hilarious mystery. And it gave me some clues for writing mystery into my novels, which most novels require! Whether you're writing a whodunit or not, there is nearly always a taste of mystery-- the reader wants to know the answer to the story question. In TUGL, my wip, there's actually a more traditional mystery than I'm used to writing, and I'm learning a few things.
1. Determine the Wants and the Obstacles
Nathan Bransford recently wrote a
fabulous post on this, focusing on the idea that mysteries are about people. Your character WANTS something they can't get right away. There are obstacles. Even if you're a pantser, it really helps to define those wants and obstacles before you start writing. They may change as you write, but if you don't have them to start with, the mystery is going to take some serious rewriting.
2. Displace Suspicion
As I'm writing TUGL, I'm so afraid that it's obvious who the thief is. Because I know who it is! And I'm placing all these clues and foreshadowings. It seems so obvious. But one of my favorite techniques is to displace suspicion: make the characters have GOOD REASON to suspect someone else. Even multiple someone else's. It makes the reader's wheels spin as they try to determine who THEY think is the thief.
3. Let the Characters Get it Wrong
This goes along with displacing suspicion. As you place clues, let the characters get things wrong. They don't have to know exactly what the clues mean. Let them go down the wrong path and suffer the consequences. It makes things more exciting, and provides a handy obstacle. Of course, you don't want them to get everything wrong. Then when you reveal the true solution, the reader won't buy it.
4. Do More than Leave Clues-- Foreshadow
In order for the reader to buy that ending, it helps to foreshadow things ahead of time. This can be in the form of clues, but it should include other things that aren't clues. You can have a character make an off-handed comment, or make a note of a character trait, or any number of things. It will make the reader scream, "I SHOULD HAVE KNOWN!!" at the end, which is much better than, "Huh?"
So, my friends, what kinds of mysteries do you like to write? What kinds do you like to read? What do you do when writing to enhance the mystery of your own story?