I'm sure there are as many ways to do this as there are writers, but I tend to do it in stages, as I have a hard enough time keeping track of my own characters and all their varied motivations as it is. First I write the "A" conflict: Bob and Carol are arguing about X, which happens to be the main conflict that furthers the plot. I get the gist of their argument written; then I go back and add Ted, who has his own agenda, to the conversation, creating a "B" conflict as well as a bit of character development for Ted. Meanwhile, Alice, on the sidelines, just wants to find the ladies'--that's "C". Then Tom chimes in--he really, really needs to talk to Carol about something RIGHT AWAY, and it can't wait; that's "D". Dick tries to get Ted, who's had a few too many, to calm down, and you have your "E". Meanwhile, Harry insists upon playing the background music at concert level, and they all have to scream over it, until somebody suggests taking the whole thing outside. And so on.
Reading the above reminded me of what takes place in play's a lot, especially comedies (Suggested reading or viewing:
Noises Off by Michael Frayn). Basically, you have a bunch of one on one squabbles happening at the same time, with an attempted attack or defence in one squabble between A & B inadvertenly tips the scales of another squable between C & D in D's favor, but A & B are on C's side, so now A, B, and C have to stop D, but then E comes in and starts squabbling with C, but D could care less about A & B and would really like that Thing C took from him back, but now E has it and both C and D are trying to get the Thing from E, who is A's best friend, so A tries to protect E from D and asks B to help so D won't get the Thing, but E is B's ex husband and she'd rather see D get the Thing than help her ex in any way, that rat bastard, and desides to break a vase over E's head instead.
The tension is built by a rising fustration level as each person takes an action.
Don't see why the same weaving couldn't be appied to a dramatic scene.