XP 60 Mixing- Left or Right???

When i record songs onto the sequencer, i noticed that not all the parts are center; some bear to the left and others right. Are there any rules of thumb when concerning this aspect of production? what types of parts (drums,bass line,melody) should go where?
thanks

You usually want the bass line in the middle. Usually the drums are centered, at least the kick and snare. toms, cymbals and other drums can be scattered around. Your main melody line should be in the center. Secondary lines, or improv solos and any background figures or accompaniments can be panned wherever you like. of course you can break these general rules for more experimental textures, but this is standard.