Is there a correct way to perform a smudging ceremony?

I have read you can mix the sage, cedar and sweetgrass together, burn them in a clay pot, and recite prayers as the smoke is washed over you and the place you wish to be cleased and blessed; I have also read the sage, cedar and sweetgrass are burned separately, as prayers are recited and the smoke is washed over you. Does it matter? Where I can get reliable information?