Does anyone have experience in photo blending?? I have a new book coming out early next year, called "The Vampire Christ" the book is ready as is the cover?? however, as this is a new genre for me, I need the cover to be 200% right, the cover in my view is perfect, but I have an idea, that I should soften the photo by over lapping or blending in another photo!! (if you get my meaning) any ideas

Some ways of blending images are masking, blend modes, opacity, blend-if sliders and more. 
The techniques can be used alone or in combination with others, so there are millions of options.
Just remember to work non-destructively to find the best solution for the images at hand.

A question such as that one makes it unnecessarily difficult to respond with a specifically accurate answer. You asked how to blend an image, which can be interpreted in so many ways. It would be best to at least reference a couple examples as to what you want to achieve in post. Without examples, you are very likely to end up receiving vague responses, because individuals will be throwing darts in the dark in an attempt to help.