To be clear I'm only talking about writing/publishing mistakes here.
It's debatable whether this first one really is a mistake but I think it's important to address, and that's waiting until I was 40 to start taking my ambition seriously - although that's not entirely true - it's complicated. I did take my writing seriously until I was in my mid twenties when I very nearly got a book deal to write children's books. And although I talked about it after that, I really didn't start writing again until I was 40. Now on one hand I'm glad because my life experience has made me the writer I am today and on the other I'm disappointed I wasted that time.
The next mistake was being so concerned by others people's opinions that I didn't publicly talk about writing. I had worked with my team for 3 years, all that time using every spare minute to write and I waited until my leaving night to tell them I was a writer. It was a mistake because by and large they were incredibly supportive.
Thinking that there was only one route to publication. I've spoken before about my decision to choose self-publishing, I only wish I'd understood it sooner.
There's been a lot of second guessing myself over the last six and half years that I've been on this journey and honestly that's been a lot of wasted time - although I suspect this might be a mistake I might continue making.
As a writer I've needed to learn that feedback is an opportunity to develop and better yourself. That being said there are people who's feedback is more important to me and you need to know when to listen and when to walk on by.
Not changing your mind - It's okay to do this and no one is going to think the worse for you. I've done this recently with the covers for my Rowan McFarlane series. That doesn't mean that I didn't like the original covers - I did, I just realised they weren't serving my books as well as they could be.
Not getting a newsletter started sooner - I've been on the go for nearly a year and I'm sure there's still more that I could be doing with it.
I'm a work in progress and as a writer I'm constantly learning and evolving and I can't imagine that's ever going to change at least I hope not. I'm sure that I could lament my mistakes on a regular basis. The most important thing about mistake though is that we learn from them and next time make different ones.