exampul_one: good tip. usually though, drums are panned to give the listener the impression that they are standing in front of the kit as opposed to sitting behind it (watching the music being played as opposed to playing it)....i.e. the snare would be panned slightly right and the hat a little to the right of the snare. toms would go from right to left.
anyhoo, when panning, you goal is to seperate instruments so every sound can be clearly heard as a distinct sound. seperate sounds which are in the same frequency range. if two sounds are in the same frequency range and also in the same place in the stereo image, they will blend and neither will be heard clearly as individual sounds. if the sounds are in a different frequency range (e.g. kick & hat), they can be placed in the same place in the stereo image and still be heard as distinct sounds because they areoccupying a different range of frequencies.
general guidlines are as follows...
bass - center
kick - center
vocals - center (often panned out for the chorus where doubles are used)
other drums & lead instruments - wider
subtle sounds, ear candy & reverb tails - hard L/R
think of it as a triangle that is pointing at you. the sounds that are at the front point are narrow and dry. as you work your way back to the wings of the triangle, the sounds become wider and wetter (wetter meaning more reverb meaning the sound appears to be further back in the mix)
experiment with auto pan as this can give some cool swooshing effects from side to side.
note that making two copies of a mono sound and panning them hard L & R will NOT make the sound appear to be WIDER. you have to use a sound which has different information in the L and R channels. or you could use a plug in which splits the audio up into frequency bands and then pans the bands L & R to make the mono sounds appear to be stereo.
another thing, playing with phase (i.e. making the sound phase incoherant) can make the sound appear to be wider than the physical speaker. this is all good and well but it is at the expense of mono compatibility. a sound that is out of phase in stereo will collaps when listened to in mono. mixes should always be mono compatible (for the sake of being radio / live show compatible) and its up to you what is more important out of stereo width and mono compatibility. generally its best to compromise and have a bit of both. or, make the effect short term so that people listening in stereo can enjoy it as periodic ear candy but mono listeners will have it pass them by so quick they wont even notice it was there in the first place.