How do I write a scene that works?

The secret to good scenes is to make them essential to the story, make them move, and don’t weigh them down with too much extraneous material.

Figure out what the scene is about. The how, why and what of it.
Figure out how you want it to end. Yes, scenes have endings just as stories do. The only difference is that, after one scene ends another one follows that’s related to the one you just finished.
Figure out what characters will be in the story. And make sure there are no more than three because few writers are good enough to handle more than three characters in the same scene without the reader getting confused. So if your scene requires a crowd, divide that crowd into segments until there are no more than three segments. Then write the scene as if each segment is a character.
Plot the scene. Beginning, middle and end.
Write the scene.