When I mix for soemone else, I find out what they envision.
I also will get the rough mixes, as they can give alot of insight as to how they are wanting to hear it.
Then, I'll try and improve on the ideas in the rough mix, as well as throw in some ideas of my own.
If the band likes the ideas I throw in, great, if not, I go back and adhere to their idea of what they want.
I can merely advise against choices I think are bad.
Because at the end of the day, it's their record. Not mine.
It's about making it better, not completely different.