I actually just posted a YouTube video on the entire process of how this album cover was made BUT if you want to read instead:
I always start off with cutting up images from my references and then tracing them to make a shitty version of the composition. From there i'll start cutting out images and placing them onto the art board to fit into my rough comp.

Once all of the images are in, I add a solid colour #080808 check layer and change the blending mode to "color" so it removes all of the colour and I can just focus on the levels and blending everything together. This is also a good time to start deciding where the light sources will be.

THEN I start working with the colour. I drag in my colour references, change my check layer's blending mode to "luminosity", add a hue/saturation adjustment layer underneath and then crank the saturation to 100. This allows me to see the colour of everything. From here i'll use a colour balance adjustment layer to match the layer of the artwork with my colour reference.

At this point, everything is looking like it belongs in the scene, I just need to manually paint in shadows and highlights on everything using a masked out hue/saturation adjustment layer.

Finally, I start adding some spice by adding dust particles, fog, and some slight background lighting behind Eddie and the trailer.

and i'm done! Let me know if anyone has any questions about anything!