Having been in plenty of bands over time, this is one of those things that is best a collaborative effort between photographer and band. Do they want something unique or something "like these guys"? If they want something unique then it needs to be a shared vision. The problem is, there are so many bands over time that to find something truly unique you usually have to steal it from someone else. Just don't grab it from someone well known or in the same country.
I've got one recommendation I always give everyone who wants to shoot anything - go to 500px and search on what it is you want to shoot and grab some inspiration. I did a quick search on "Rap Artist" and "Rap Group" and there are plenty of images there to both provide inspiration and to make you say, "Yeah, I really want to avoid that pose". As with all band photos, stay away from brick walls and train tracks. It's the magnet that pulls every band and photographer there only to produce the photo that screams "Your band sucks!!"