There are two sides to writing a story–writing it and editing it. Writing is exploring your story to get all of what you have imagined out onto the page. Editing is taking that and polishing it, or for most of my stuff, cutting then replacing.
I often find myself rewriting large parts of my story, and I have decided that, often, this is actually a better way to work. When I rewrite, I already know the story I am working on. I know where it is going to go, probably, and I also have a good idea of where the problem points are. By rewriting it, I can focus on where improvements are needed.
These improvements come down to things that I tend to hurry through in the first draft in my drive to get the story down on the screen. Things like suspense, background, character traits, and simply drawing connections between things. I also always find a place where two minor characters can be rolled into one or where a character can play an usual role later on.
You may wonder why rewriting is better than revising. The reason is simple: ego. You wrote these wonderful words on the page the first time. There are certainly some very clever bits. Can you just cut them out? It is hard. It is even harder to rewrite scenes that you spent ages developing, although you know in your gut they need to be completely redone. That is another kind of writer’s block. An ego and laziness block. It is easier and safer for your ego to just tweak them by revising. Don’t do it though.
You know you could rewrite them better. Go ahead. Give it a shot.