okay... often times you can create a very wide effect by panning certian frequencies of (say a pad) sound just a little bit (fl studio equo lets you do this with ease). also, when you build a sound in a multiple oscilator synth, it's good to pan the oscilators a little bit away from each other sometimes to create some stereo range (DO NOT bother using so called stereo enhancers, cuz that's wack). also, in your synths, many times you can pan the filter outputs, which also creates some wideness...
making sure your bottom end is centered, and that the sub bass is MONO is very important... but do not do this with your regular bass sounds, you'll kill their "fattness"
a little panning on the hats and percussion is cool, but not necessary, and please don't overdo it... sometimes using a stereo phaser or flanger can add the stereo range you want.
to the guy who talked about club systems... club systems are in stereo dude, it's not like they're running through one big speaker.
david