I’ll just add my name to the list of Matheson fans. I discovered his writing after the most recent film adaptation of I Am Legend. I’ve read a number of his short stories and am still working through them.
Stephen King’s “On Writing” is a great read whether you want to write horror or not. I enjoyed his “From a Buick 8” a good deal, and that was after not having read any of his work for quite some time.