A trap that many dissertation writers seem to fall into is to start off a writing session by re-reading what they wrote. I think that reading back a paragraph or two makes sense and can help you get back into the rhythm and flow of your writing. What doesn’t make sense is to spend your whole writing time re-reading what you have already written. For your purposes, writing time should be kept separate from reading time. It’s too easy to get caught up in revising and editing what you’ve already written- especially when you should be writing new material. Always focus on writing new material, first. Aim to draft the full dissertation as quickly as you can. In this way, you can be more certain that you’ll actually finish as planned.