I have a tiny friend who'll often just ask if she can switch places if a tall person moves right in front of her (she's not advocating a height based layout on the dancefloor, just for the times it's just one persons back that's her view). I'm tall, I'll try not to block people's views but it's basically inescapable.
As for all these ideas that we should fill up the dance floor in the order we arrived are nonsense. It's a gig, seeing the band is great but hearing the band is what you're there for. Dance, enjoy, sweat, move. Heck if someone offers to shake your hand you don't have to shake it but you can see it as a friendly gesture as opposed to some breach of etiquette. Live music is about experiencing something with other people who love it too