Now that I've come up with a title for my post today, Glenn Miller's "In the Mood" is in my head. No, I'm not that old, but I grew up listening to it, thanks to my dad.
Sometimes it seems that characters in erotic romance get "switched on" pretty instantly. They just have to smell a guy and they're ready to go. I know I've written scenes that go that way, but isn't that part of the fantasy of erotic romance? That we buy into this dream where a drop-dead (and occasionally undead) gorgeous guy gives the heroine (i.e., us) a smouldering look and we get all hot and bothered?
It's a broad generalization that isn't always true though, in writing. I know my characters don't always get aroused straight away, but I lead into it by having them banter in a (hopefully) witty way; or by arousing partners by playing a kind of "Truth or Dare" game.
In MADE FOR SIN and SHOW ME watching others having sex becomes a turn on for various characters.
Then there's anticipation. I use it when my hero and heroine have already become intimate. I write historical, so there are long dinner parties where they're forced to sit apart and make polite conversation with other people while casting surreptitious glances down the table at the other. Or they have to dance together, hands touching, hands touching the upper back, joining arms, close enough to have a whispered, teasing conversation, but not close enough for anything else. Not in public anyway.
Alas, there was no dirty dancing during the Regency period (unless you want to include the waltz), so everything has to wait for a private time.