I've been waiting for months to get my hands on a copy of Skillman's book "Writing the Thriller." It's tough to find since it hasn't been reprinted in years. And now, after finally reading it for myself, I'd say that if you can locate a copy, do it.
The most helpful parts of this book for me were the sections explaining the interplay of conflict and tension in plot structure, specifying the differences between mysteries and suspense thrillers, and the tips on how to avoid the mid-novel slump by improving your pacing.
Professional writers will also enjoy the nuts and bolts essays by such writers as Tess Gerritsen, Michael Connelly, and Clive Cussler that appear in the second half of the book.
Novelists--the next time you see this book available, buy it!