I just read this:
petapixel.com/guide-to-creating-and-using-texture-layers-in-photography/
A quick and dirty example
I have a spider shot against a plain tin background:
I stole a texture layer from the article:
Then, in the GIMP, I resized it same as the subject layer, selected 80% opacity, 'Burn' mode, and messed with the texture layer a tad:
The result:
What do you think?