One sexually charged thing you sometimes see in non-porn sex scenes is an attractive lady flirting and smiling with a guy, even as he prepares to penetrate her. And then a sudden cock thrust from her guy wipes off her smile and changes it into an expression of lust and surprise.
I think this kind of thing would look pretty good in a porn movie too. And it won't require much acting from the lady. All the lady would need to do is smile at the guy and talk without knowing exactly when this guy will penetrate her. His sudden cock-thrust inside her will be a genuine surprise for her. And it will naturally change her facial expression because of all that new and sudden sensation she feels from the guy's penetration.
I've seen something like this a long time ago, where a guy spilled his cum after having anal sex with a lady in the doggy position. Her asshole was gaping, he kept rubbing his dick on her cheeks, and she kept urging him with a lewd smile to plunge his cock back inside her ass. He didn't comply for a while. But then he suddenly plunged his cock inside her gaping asshole and made her feel his full size all the way to his balls with a few good thrusts. Her lusty yell and the change in her facial expression is something I still like to remember with fondness. Because this was a one hot moment you don't often see in porn nowadays.