Avoid tangents. Stay focused on your writing.
When you have a big writing project like a dissertation, it’s easy to let yourself get distracted. The best way to keep writing is to keep focused. If something is not a direct connection to what you’re writing now, ignore it. Remember, you’re not writing a manifesto. You’re writing a specific, narrow text. There will be time to write other things later. Right now, you need to focus on the topic at hand. Your writing coach can help you focus.