I have come across a few books about voluntary possession with spirits, but almost none on deity possession. Any good suggestions?
The work of Marc Allen Smith heavily involves invocation of the deities he works with, Hekate, Lucifer and Belial. Otherwise, it’s not really a thing that I’m aware of.
Some nice possession rituals? Enoch Petrucelli’s book: the Black Witch
Raven Kaldera touches on it heavily in his Shamanism books.