Let's look at an example:
I turned around and saw him standing in the doorway.
Well, unless he is in a wheelchair, or for some reason he wouldn't be standing (maybe he's been hobbled like Paul Sheldon in Misery and he can only drag himself from place to place), why does a reader need to know he's standing? It'd be a miracle if he was wheelchair-bound and suddenly he stood in a doorway. That's important information in that instance. But just a guy in a doorway? What else would he be doing besides standing?
Okay, maybe he's leaning against the doorframe. Maybe with a smile on his face I can't resist. Or maybe he's crouched slightly, gun in hand and ready to shoot me (or maybe the guy who's holding me hostage - yeah, that's better).
I turned around. He leaned against the doorframe, a smile on his face. Not just a smile, but that smile. The one that got me every time.
or
I turned around. I barely had enough time to register the crouched form of a man before I saw the gun come up and heard the kidnapper fall to the ground.
See? No standing needed.
Give me some action!
