The perfect scene is the scene that gives you just the right one or two details that you need to get a sense of the whole thing: the atmosphere, the setting, and what the characters are thinking or feeling, both in that moment as you enter the scene and throughout the scene as you take them (and their changing emotions) through it.
So, how the heck do you do that?
One way that works for me, since I watch a lot of movies (and, let's face it, I'm addicted to my favorite TV shows - I even get all snappy and irritable on rerun weeks, and I get all giddy when a new episode is coming up, and OMG SUMMER IS COMING SOON AND WHAT AM I GOING TO DOOOOOO??? *ahem* It might be a little unhealthy.), is to think of the scene as if it were being played out on-screen.
You know how often new scenes start with a close-up of something? Someone's hands fidgeting with the hem of their skirt, or a vase of half-wilted flowers on the side table, or something? Well, those are the same details you can start your scene with. Of course, it's probably not a good idea to start with those examples, because they're clichès, but you should think carefully about the tone you want to set, because the details you start with will dictate how your reader approaches each scene. Choose the one or two details that you would zoom in on if you were the director and this were your show.
And as I move through the scene, I picture it in my mind, and I write the details that my mental camera zooms in on. If the protagonist is feeling cornered by an intruder and needs to get away, in my mind, the camera zooms in on her grabbing the vase of half-wilted flowers and tracks the vase her as she hurls it at him. So, that's the detail I focus on; not what her body is doing, or what he's doing to dodge it, but her hands on the vase of flowers. (Again, clichè, but you know what I mean, right?)
So, that's how I approach it. How about you? Do you write with your zoom lens attached, or do you have another method? What works for you?