One thing that you must stop doing is reading every blog post, article, and book about THE ELEVENTY ONE THINGS YOU ARE DOING THAT MAKE YOU A HORRIBLE WRITER. If you read all of these articles you will inevitably see that you are doing that, and that, and that, and oh dear God even THAT wrong. You will terrify yourself into a state of being unable to write at all. If you are doing it, if you are reading these things, stop it right now. If you aren't doing it yet, don't start.
One of the many highly contentious debates amongst writers is plotting and outlining versus just writing, seeing where it goes, and spending more time editing later. If you find yourself spending so much time outlining and filling index cards with character descriptions that you never actually get around to writing line one of chapter one, stop it. Stuff it all in a box so you can refer to it later if necessary, and then just start writing. A sentence, one sentence. All the outlines and note cards in the world will not serve you if you cannot put one sentence on paper. I am not disparaging outlining. Many writers use it fantastically to their advantage. I never could. I spent years outlining and making notes and making little character cards and never got a book written until I just sat down with a random, out of order scene in my mind and ran with it. Honestly, I do have to refer back in my manuscripts sometimes for full names, former names, and other details, but I'm okay with that. I keep buying little notebooks and telling myself I'm going to start making notes...but I'm almost afraid to stop what I've been doing, and break the spell.
If something is stopping you from actually writing, put a stop to that thing. Put something on paper, or your hard drive, or whatever, and then fix it later. You can't revise it if you never write it.