Some writers can sit down, open up a page, and write. Others need a little prep work before diving into a new scene. I'm one of the latter, and I've found I'm a lot more productive if I take a few minutes to figure out what I'm going to write before I write it.
There are all kinds of ways to plan your scenes, but consider figuring out the plot-driving elements first. Knowing your protagonist's goals, their motivations, and the conflicts of the scene will make it easier to move the story forward. If you're not sure how it ends, you might think about taking a little extra time at the start to figure that out. Often scenes get stuck because the writer doesn't know the next piece of the plot to move the story to the next scene. How this scene will setup and transition to the next.
