Okay, I know I'm going to sound really lame. REALLY REALLY lame. But bare with me. Please? I used to write a lot for fun. I learned how to read when I was two, and how to write when I was three. I loved it. I wrote some terrible poetry, but writing was a great outlet for me. I loved it, with every fiber of my being. Writing was my one true love. This love however, didn't last very long. I started to notice other writers and the way they wrote. I started to compare myself. I saw these wonderful writers with their eloquence with words and how I was just so....inadequate. My thoughts because so twisted and dark that I began to grow more and more frustrated as the days went on because I was realizing I was an awful writer. I could no longer finish anything anymore. And that is when my self esteem went down the drain. My motives were no longer to express myself but to impress myself. I get very emotional when writing now. If I do write, I'll get angry with how horrible I think it turned out or not bother completing it. If I'm writing on paper, I'll rip it up and throw away the paper. I just wanted to know how to start writing again without judging myself?
Compare yourself to your previous self, not others. Try to write better than before. That's a reachable goal. Don't throw away all you've written, keep it as a milestone. The next one will be better. If you can't seem to finish anything (I know that too), write something shorter. A short story. A short short story. A single scene, maybe. As short as you can complete.
As a writer, don't ever stop pushing yourself to get better but it's not fair to compare yourself to other seasoned writers. Everyone starts somewhere. It's very rare to find a writer who picked up pen and produced a work of art out of the box (not impossible, but rare). As IDLE said, compare yourself to your previous self. Look at what you've done and look to do better with each effort. You biggest competitor will always be yourself.
Look at your work from how you were when you first started. You are your own worst enemy, they say. Think Rowling or King care that someone else can write better than they? No. All they care about is, 'Can I write better than I did the last time?' Remember, the master was once the apprentice. Someone had to teach them how to write.
Instead of comparing yourself in a negative way, try and see what similarities you have with the other writers, and just try and see it in a positive way, don't put yourself down about it. If your style of writing is true to you, then that's better than you trying to copy other writer's style and readers will love it
I would be a hypocrite if I said, "Don't compare yourself to other writers." Fact is, I'm only human, and I'm inclined to draw some comparisons whether I like it or not. One thing to keep in mind is what your original intentions for writing were. You said so yourself that you began this whole process because it was loads of "fun" for you, right? I'm in the same boat as you. Sure, it would be nice to put something out and make money off of it. But let's not forget that we did this because we enjoyed it, so be selfish and write it like how you'd like to read it. Stop caring about what other people will think. If I kept worrying about how other people are going to feel about my writing, I'd probably have quit ages ago. In the end though, we can only give you advice. We can't make you stop judging yourself. That's going to be your own battle to fight. In all sincerity, the best of luck to you.
Always remind yourself - every famous writer was once an amateur. They were nervous, scared , felt self doubt and worried that they would never sound as good as the writers THEY admired. A good many popular writers had friends who rescued drafts they were ready to burn out of sheer insecurity, and frustration. Don't put writers on a bar to reach, it's not a contest - writing is about finding your own voice. Use writers to learn from, gather techniques and inspiration from their work . And give yourself a break! - I've written some truly dreadful stuff. I can laugh at it. I can see myself growing as a writer - which you never stop doing. I don't think there's ever a moment when a writer says I have arrived, I'm a writer. They keep striving to do better, whether they're published or not. Go back to loving writing, skip worrying about not being good enough - that's stopping all progress, instead work on getting better. Something you can do.
A wise person once told me, "The moment someone says that they've learned everything there needs to be learned, that person has failed. You never stop learning, never stop growing." Keep writing the book you want to write.