Kick / snare always center
Toms high to low start 50l to 50r
Overheads pan to a realistic spread, nothing is ever truly hard left or right as it bleeds. Go 60% one side at most if you use single samples. If you are stereo micing real cymbals pan the stereo pair 100 l 100 r.
Exporting a mono wave and duplicating it to pan hard left and hard right will result in the exact same sound as just leaving one of them centered.