There are a lot of things that can drain your creativity as a writer, but one of the worst is trying to edit while you are writing.
One of the important things to learn in writing quickly as well as writing effectively is not stopping and second guessing yourself about choices of words, sentence structure, spelling or grammar. Those are all things that can be fixed after the fact.
When you are writing your first draft, let yourself run free. Put down what comes out of your brain immediately. It’s always possible to go back and fix whatever it is that you think is wrong.
If you stop yourself from running free, you may miss creating something really different and interesting.
I will often write vital scenes without stopping (or stopping only a little). I want to get that rush of fresh thoughts down on the paper, especially when it comes to dialogue. Having the right pacing and words in dialogue often come easier when you just let it flow. It’s easy to go back and fill in what may be missing if you’ve got a good rhythm to your dialogue.
So – shut down your internal editor for that first draft. Let yourself explore new things and pour your heart out onto the paper. There will be time enough to fix things once you’ve finished the scene.