There’s a lot of great writing advice out there. The best advice comes with the caveat that it is what works for the author who wrote it and may, but not neccessarily, work for you, too.
This advice includes things like restrict adverb use (or more extremely, NO ADVERBS EVER THEY’RE BAD YOU’RE A MONSTER FOR USING THEM), always use simple dialog tags/vary dialog tags/never use dialog tags, make sure all your fluff advances the story, make sure all your characters have a clear arc, etc. etc.
It’s good advice, but it may not be the best things to keep in mind as you’re racing to accomplish 50,000 words in 30 days.
1,667 words a day for thirty day is not, in itself difficult. The real challenge during NaNoWriMo, in my opinion, is having those thirty days in November. It’s a busy month, particularly if you’re an American who celebrates Thanksgiving near the end of the month. If you add in Election Day and Veteran’s Day, plus holiday shopping, maybe even Halloween tear-down, that’s a LOT of demands on a would-be author’s time.
The demands on an author’s time in November are one reason I advocate building up a buffer early in November. As the holidays approach, time becomes more and more valuable. So, my advice if you want to increase your speed, is to take all that advice about making your writing better and chuck it out the window.
Write your story.
Ignore the rules about what makes writing good (or even acceptable).
Editing & revisions later will make your writing good. If you don’t get a story written down, there won’t be anything to edit.