I often hear people say that if they knew they were going to live this long, they'd have taken better care of themselves. I think writers find many areas of the business where a little forethought (or listening to the advice of those who've gone before) would have saved them work and frustration.
Early on someone advised dating the file on a project in the file name. That way you always know which version is the most recent and, ostensibly, the best. I didn't do that for a long time, until changing between my PC, flash drive, and laptop plus hard copies printed on front and back of sheets of paper made me crazy. Now I date everything and can easily find the last version I worked on.
Another piece of advice I ignored was the collect-emails-from-everybody rule. I guess I was shy and didn't feel I had anything to say to the dozens of people who came to hear me speak at each library. Now that I have a second book coming out, it would be nice to be able to tell all those people about it.
I'm sure there are lots of "should haves" and "could haves" for each author, and I've said here many times that there's only so much a person can do. No sense crying over spilt milk, y'know. As long as we keep learning, we aren't dead yet. And what doesn't kill me makes me stronger.
There. Have I thrown enough platitudes at you for one day?