Many folk have written about placement of instruments in music production, but before I discuss this, I'll just mention about LFO in synthersizers, LFO means Low Frequency oscillator.. this makes the synthesized signal appear to move (or modulate) this is deemed necessary (by those that know) to make the sound more interesting...back to the original point...Movement in a mix.
I often hear songs that are brilliant in every way, but something is missing, and it might be that there is no Sound Stage dynamism during the song. Mybe a better way to explain it is that nothing moves about from where it started in the Stereo Sound Stage.
Now don't go moving everything about all the time, one wouldn't experience that at a live gig, but subtle interesting moves of instruments keeps the whole piece interesting.
A very simple example is a Guitar solo that moves slowly from L to R, while everything else stays where it is. this can be done using Automation of the Pan knob, but there are auto panners out there that can do that a little better (and easier). Soundtoys PanMan can do allsorts of tricks, keyed to the bpm of your DAW, very cool. You'll find your ears go wandering in a nice way.
Another great tool is Waves Doppler, which emulates the Doppler effect (the police car siren changing pitch as it goes past)...most Waves stuff appear at $29 through the year, worth a punt, could be interesting on an EDM drum track starting up from a drop, imagine too if it were used with the PanMan?
Anyway give it some consideration it if your mix sounds a little boring...
Hope it helps