Continuous Improvement.

Back in my corporate days, I worked in quality.  Without getting into too much detail there is a concept in quality called "continuous improvement." This is where you set up systems that ensure your processes and procedures always get better yielding fewer mistakes, fewer off-spec or off-grade product, and saving the company money.  The "Plan, Do, Check, Act" cycle portrayed at left was one of the tools used.  Because if you don't continuously improve, your competitor who does will sell better products for less money and take your customers away costing you profits and perhaps even killing your company.  Think Japanese automakers versus U.S. automakers in the 1970s and '80s.  Japanese industries took these precepts to heart after World War II which is why in less than a generation they went from "They make crap" to "They make the best stuff."

As a writer, you should also be striving for continuous improvement. I know I do. Even best-selling authors are very likely trying to write better all the time.  If they don't, they won't stay best-selling very long (this is, I think what happened to Tom Clancy; he got lazy).
For example, after my first couple of novels were published ( Hammer of Thor and Agent of Artifice ), just for fun I went to this word cloud website and made word clouds from the edited manuscripts.  And here's what I found: Word Cloud for Hammer of Thor
Word Cloud for Agent of ArtificeAnd I noticed that I apparently used the word "looked" a lot.  So now I'm on a mission to eliminate it by instead of saying "He looked" saying "He glanced" "He stared" "He scowled" "He squinted" pretty much anything but "looked."
Then my writers' group told me I should avoid adverbs.  So I do that, too.
Lately I'm on a mission to avoid the word "seemed" because I have noticed I use it way too much.  I don't have to say "The room seemed charged with her power" (a line from Gods of Strife ) but "The room was charged with her power."
If you aren't striving to improve you're writing (and I don't care how many books you've sold) you aren't going to get better.  And all the writers who are working hard to improve their writing are going to be a better writer than you.  And you'll be left in the dust.