As an author, one can never stop learning,
never stop researching, never stop working to improve one's craft. That includes future work, work in progress and past work.
That's not to say you should go back and rewrite previous published work - unless of course there's a glaring flaw that needs to be repaired. And again, of course, you don't learn that at first, either. So while you're bound to make mistakes, and I've made my fair share, don't stop writing - it is the very definition of on the job training.
Along that vein of progress, it is fair to say, if you keep your eyes open and aren't so antisocial that you ignore your readers and other authors, you can build a network of people you can rely upon for assistance, honest opinions and even hands-on help if you need it. I am lucky, blessed even, to have that network - many who have become downright friends, people I am happy to collaborate with. Some of them have helped me over story blockages, offered editing assistance, and most recently, taught me some things I didn't know about formatting and the finer points of getting table of content entries to digitally function they way they're supposed to. Thanks, Aaron.
While writing my 2nd book; Wings of Steele - Flight of Freedom, I realized I was writing better, cleaner, smoother... I had found my author's voice and I was considering backtracking to Book 1 and rewriting it all over again - at least a good portion of it... until I was approached by Harper-Collins. They offered me a three book deal... the first book and two more, sight unseen. Color me speechless. But it was a sign I had done something right, the 1st book was good enough for them to approach me. So, after I completed the 2nd book, I did go back to Book 1 for some work to make improvements, and while I did do some rewriting, it wasn't an all-out effort like I had originally considered.
There is something to be said about having an early benchmark of your work to compare new efforts to, something to gauge your professional progress... But some things, like better formatting, should be retroactive - keeping everything, new and old, to a functional uniform level. For that reason, I have, with assistance from a member of that aforementioned wonderful network, happily brought Books 1 through 3, up to a functional level of Book 4.
Now it's on to Book 5... but that's for the next post.