This is a funny thread for me, only because our banner came floating down onto the stage in the middle of a song at this past weekend's gig!
Damn cheap-ass duct tape!
Get a roll of Gorilla Tape. That shit will stick to anything. We bought it when we had a couple of venues with just tumbled stone/brick backgrounds and there was no other way to hang it.
We have grommets and everything else mentioned. Depending on what's available to hang in on or attach it to, we use zip ties, thumb tacks, gaffer tape (if it's a delicate or painted surface), or Gorilla tape. We haven't come across a venue yet where we weren't able to hang ours except one where the stage was in a corner of the room and the backdrop was huge velvet curtains