I used to be hard on myself when first writing a new blog post or chapter of an ebook. I would never get anything accomplished.
Your first draft should suck.
First, understand that everything you create is part of a draft process. Don’t create something thinking it will be perfect from the start. It won’t. Ever. All you have to worry about is getting all the thoughts out of your mind and onto the paper. It’s easy to get distracted with each sentence, deleting words, editing sentence structure. Don’t worry about these things until much later. These things will stop your flow of writing just so you can go back and wordsmith a sentence. When you catch yourself rereading sentences and trying to perfect them you should ignore that first instinct and just keep writing.
Vomit everything out. Don’t delete anything. There are things I normally would delete because it doesn’t pertain to the post I’m working on. I found when I save all my thoughts most of them end up being used on other posts on my blog. Rarely will any content be wasted. I save a lot of time in the long run by keeping all my thoughts because I’m never starting from zero.