Mix imagery is important.  The overall width of the stereo field and how instruments are distributed within that area is an important mixing tool.  Likewise the space you create to put the vocal in (the reverb setting you will send the vocal to) is important not only in terms of defining the overall mix space but also in enhancing specific feelings in the vocal.

Music should always be discussed with subjective as well as technical terms.  Sometimes a visual description is better than a technical analysis.  Once when I was mixing I could not properly place a specific instrument to a client’s liking until he described a visual scene to me and told me to have the sound act like one of the elements in the scene.

Some mixes are dynamic and involve quite a bit of changes to the instruments as the song progresses from start to end.  Some are more static in that once the instrument sounds are established there is not much change occurring as the song progresses.  Some mixes contain recordings of instruments that are already changing as the song progresses (perhaps getting louder and softer at the performance rather than needing it done in the mix).  In such cases, although the playback volumes of each of the sounds may stay exactly the same setting from start to finish, the interweaving of the built in changes in each track will give the whole mix a very natural movement.