Best description i ever heard regarding the stereo field is this...
Instead of trying to understand it with sounds, try to visualise it. Imagine your music as a room. There is a front, back, left and right. When producing your tracks you need to try and fill these areas. Obviously panning can help with the left and right. But mono and stereo can help with the front and back feel to the tune.
Try getting two synth sounds, put one in mono, and the other through a stereo enhancer. You will notice that the one in mono, sounds like its behind the stereo one.
So yo gotta try and fill all that space. Sub bass and kicks usually always mono. Things higher up the spectrum like hats can be panned left and right. Pads can be either mono or stereo enhanced depending on what you are aiming for. Lead synths etc can be panned, mono, stereo.
Basically try and keep your lower frequency elements centered. And as you go up the spectrum, try and widen them more.
/\ great description
some ideas for Stereo Field enhancement (besides panning)
Chorus, play with diffrent settings
Filter Delay, if you can set the delay to ms instead of beat, you can do all sorts of interesting things with the stereo placement of your sounds, experiment
Reverb, Hi-Passed very wide Reverb can really bring your stereo field to life
Bass, tweek your FX, esp things like Chorus, Phase, even Verb (on bass?! yep!)
the important thing for playing with Stereo imo, is movement, get sounds talking to each other/ bouncing off each other, moving from left to right, mono to stereo....even up and down, behind and in front of the listener
Look up Doppler effect, and see how you can use it to create 3D spaces in your music, moving filters and panning can create some awsome effects, you can get Doppler plugins, for eg WAVES do one, but you dont need that, you just need to understand doppler and use your filters and other FX creativly