When mixing a song it can help to visualize the mix as a 3D cube. EQ (bass, middle and treble) is the front face of the cube going from the bottom (bass) to the top (treble). Panning places the instruments in the space between the left front wall and the right front wall. Volume goes from front to back with the loudest instruments at the front. Reverb primarily provides the front to back (and side to side) instrument locations (depth) within the cube.
Compressors and equalizers can make an instrument seem more upfront as can short delays (long delays can make the sound seem more distant and delays can also make it seem wider depending on where they are placed).
The art of mixing involves the creative placement and movement of the instruments within this 3-dimensional space.
This concept is illustrated extremely well in David Gibson’s excellent book. “The Art of Mixing: A Visual Guide to Recording, Engineering, and Production”.