David Mamet explains what you must do in every scene:

SO: WE, THE WRITERS, MUST ASK OURSELVES OF EVERY SCENE THESE THREE QUESTIONS.

1) WHO WANTS WHAT?
2) WHAT HAPPENS IF [THEY] DON’T GET IT?
3) WHY NOW?

And reminds you that it doesn’t come easily:

THIS MEANS ALL THE “LITTLE” EXPOSITIONAL SCENES OF TWO PEOPLE TALKING ABOUT A THIRD. THIS BUSHWAH (AND WE ALL TEND TO WRITE IT ON THE FIRST DRAFT) IS LESS THAN USELESS, SHOULD IT FINALLY, GOD FORBID, GET FILMED.

IF THE SCENE BORES YOU WHEN YOU READ IT, REST ASSURED IT WILL … BORE THE AUDIENCE, AND WE’RE ALL GOING TO BE BACK IN THE BREADLINE.

Along with Chuck Wendig’s post on structure, this is required reading, writer friends.