Obscurus
I read a ritual in a book once that called upon a deity by symbolically reenacting her myth of descent into the underworld. That might work too.
Innana/Ishtar?
Yeah, I've come across a few sources myself that recommend 'developing a relationship' with one god(s)/goddess('). Which would be mostly whats been said, learn about their myths, feats and failures, relationships to other gods, and correspondances. But it also recommends something like pray and talking to them regularly, and such so that they can get more accustomed to you too. I think its a pretty good idea, but may not be as practical for a being you may work with once.
As far as a pick up line, I guess I'd use something like, "Hey, big, deep, and inspiring, wanna join in an unholy union that will cause the cosmos to shake and tremble before us?"