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.