On my journey toward publication, I've made screes of mistakes. I started off completely ignorant as to the process. When I finished my first novel, I looked up the address of the publisher that published my favorite books, and mailed off the manuscript. No surprise I got it back a few weeks later with the note 'we do not accept unsolicited manuscripts'. Actually, getting the package back was kind of a surprise. I mean, posting something that big is expensive!
By the time I finished my next book, I knew a little more (only a very little, mind) and rather than blindly sending to a publisher, I entered it into a contest. Not surprisingly, I didn't win. The book hadn't been critiqued or edited much, and really wasn't ready to go out, something I didn't learn until I discovered WDC (writing.com) and joined a critique group.
I had no idea about agents and what they did, and the first query letters I sent out were atrocious. I made every mistake in the book - not addressing them by name, not telling them what the book is about, focusing on all the wrong things in my bio - and no surprise, no one bit.
When submitting short fiction, I've made my share of mistakes too. I've submitted the same story to two venues when one of them doesn't accept simultaneous submissions. I've submitted stories to publications that are so wrong for them it's not funny. Reading the publication before you submit to them is always a good idea. Sometimes the submission guidelines are a little vague as to what they are looking for.
But for all the mistakes I've made, I've learned a lot. I feel that I have gained the knowledge I need, and keep gathering more, each and every day.
What are some mistakes you've made? And what did you learn from them?