I've come across some great tips the past few years for writing mysteries. Although genres have become fuzzy there are still basically two types of mysteries: Hard boiled and cozy.
Hard boiled mysteries can be likened to Law and Order. They usually take place in a well known city and the suspects are spread out. Cozy mysteries tend to take place in a small village or confined area like Agatha Christie's novels.
When I first started writing a novel I picked out a cozy mystery from a well known author and studied it. I outlined each chapter to get a feel for the way the plot was woven. This doesn't mean you're going to copy someone else's work, you just want to get an idea of how the characters work together. I also keep a notebook with me when I'm reading and if I find words or a description I love, I write it down. Again, you're not going to copy, but it does show you how to make the words stand out.
Two resources that have been the most helpful and not only for mystery writing are:
Margie Lawson's Deep Edits lecture. You can attend classes online or purchase the lecture notes. The lecture notes are great. Margie is a great teacher.
Writing the Breakout Novel Workbook by Donald Maas
Other links you may find helpful:
Detective's Log
Writing the Cozy Mystery by Stephen P. Rogers
The Mystery Genre
Exercises for improving dialog
Cause of Death
Plotting the Mystery Novel
