One of the most common questions, complaints, and concerns I hear is that a writer edits while they write, or stops and edits a chapter before moving on, and so on. They get stuck. Stephen King and so many others recommend you do not do this–do not start editing until you have your first draft. Then edit all you like. In fact use placeholders, such as (in fiction) “crime scene.” Then you can always go back and talk to cops about crime scenes and so on.
Not only does editing as you write slow you down or stop you, it can mess with your style and voice. Did you know you write “like you’re reading?” It’s true. Best if you read a particular author(s) exclusively if he/she/they pertain to what you’re working on. It will come through. Ever find yourself starting to use a slight southern drawl when in South Carolina, or a definite dialect when in New York? We are influenced by what we read and observe. Another reason to get quickly through your first draft.
For non-fiction, I’ve found it best to overshoot your word-count target. If a book is largely based on interviews and we’re writing a 50,000-word book, best to have something line 70,000 in transcribed words (not including all the questions and so forth).
Editing is about taking away and making clean and concise more than about adding where needed, and then about organizing and perfecting.
Anyway, a simple tip, but an important one, and a hard one for perfectionists to follow!
Recommended reading, On Writing by Stephen King