Good photo reference and prep work makes a lot of difference in an illustration.   Here, I’ve googled reference for tombstones, graveyards, a 45 pistol and an ancient ceremonial knife.    I’m also the model for this, shooting pics with my Iphone camera.   Quick and easy to do.   I find , like every other illustrator, that good reference adds lots of detail you wouldn’t necessarily imagine, and once you set it up makes the actual drawing go very fast.
Here are the digital pencils, which took me a couple of hours.   I found a really cool photo of trees in silhouette against a night sky.    Once approved by my publisher, the drawing will be  digitally inked and colored.    By the way I came up with the logo for this cover also.    “The Grave” is a spooky vigilante series set in the nineteen twenties.