Be creative. You should try and give everything its own space in the mix, in terms of panning, but also in terms of EQ and dynamics. A lot of people (here and elsewhere) will try and give you a list of rules for "WHERE THINGS GO." Don't believe them. Use your ear, and find what you think sounds right. Listen to albums you (or your client) are fond of, and figure out where things are panned. If you like it, do it. For myself, I highly recommend anything which has been mixed by Tchad Blake. He is very unconventional about how he pans, but also very creative. But mostly, listen to albums YOU like, and use what you hear there.
Light
"Cowards can never be moral."
M.K. Gandhi