Disclaimer B: I'm no where near done making mistakes -- some of which are likely to be epically stupid and more than a little mortifying.
That said, the stupidest thing I've done on my path to publication is ... failing to network well.
"It's not what you know, it's who you know."
I hate that saying with the sulfuric fires of a thousand dragons. The extreme introvert in me loathes to admit part of the assertion is true, yet not in the way of the inevitably nepotistic inference. The lie, of course, is that I can be successful and clueless. Bullshit. In the world of genre publishing, whoever the business fails to weed out before the book releases, the readers nail in a heartbeat.
That leaves the stomach-twisting truth:
"It is who you know."
The most wonderful and terrifying thing about genre writers is they are willing to create opportunities for folks who have proven to have a clue about the genre and a modicum of social skills.
How does that lead to my stupidity? I've met marvelous people in my quest for publication. Those marvelous people have either offered introductions or actually made the introductions to even more marvelous people.
I fail to do anything to develop those relationships past the introduction.
Do NOT, not, not, not, not, not repeat my stupidity. Do take two minutes here and five minutes there to drop a line to those people you have been most fortunate to meet. Let them know you're thinking of them. Don't wait six months to follow up on an introduction. Say "hi" more than once a year. Do NOT contact them only to ask for something.
How do you maintain career acquaintances, dear reader? What is your one DO and your one DON'T?