the basic way would be to use one of the actions out there. @jbmanning5’s here or the one that sean murray did on facebook. outside of that, it’s a bit of an art form. you want to get contrast without losing detail. hard to explain.
but if you have a really high quality original image, running JB’s script will do the work for you. if you picture is of lower quality, it may take more.
I really struggled with the processing in the past. I got one really good engrave of my recently deceased father in law. now I have to get my daughter’s best friend’s dog done.