If there is one thing I can urge you to do that will make the biggest impact both on your writing output and the quality of your work it would be to let go of the myth of perfection.
This is easier said than done. In fact, you may be thinking, "Pfft! Perfection isn't my problem. My writing is crap!" But even that is a value judgment rooted in perfectionism.
There is nothing wrong with having good taste. There is nothing wrong with trying to meet the standards of our good taste. There is nothing wrong with striving to make our writing better--until, well, it keeps us from making our writing better.
In the pursuit of perfection we can allow the rules to rule us--rules of grammar and storytelling conventions, of when and how to write and under what conditions. ("I must have three hours of uninterrupted time!") There are ideas of what it means to be a "real writer" that are pretty destructive, too.
Perfection can lock us into a revision loop. Our sentences are worked to death. They march across the page like dutiful soldiers, any liveliness or personality stripped away.
Perfection keeps our creativity under wraps. We are in a near constant state of judgment of our own work. We don't allow ourselves the freedom to find out what we really want to say for fear that we'll say it the wrong way.
I have seen perfection flatten the most delightful prose. In the most virulent cases, perfection can keep writers from writing a word.
Instead of perfection, aim to shape your words into something that sparks an emotional response in your reader. Forget the rules and all the "shoulds." Play with words and ideas as a painter plays with color, textures, and perspective. Let prepositions land at the ends of sentences. Go wild and write a sentence that fills a page. Don't write like a Writer, write like you. Play until you discover what you write like.