The Dissertation is a Marathon not a Sprint!
A surprising number of doctoral students, perhaps because their course work is so carefully scheduled by the university, think that the dissertation is a sprint to the finish line. Nothing could be further from the truth.
One good analogy is that a dissertation is like a marathon.
You must start slowly and set a steady pace that will enable you to sustain a high level of effort over a long period of time if you want to have a realistic chance of finishing. Think of yourself as a tortoise, not a hare.
In practice, this means doing some of your dissertation-related work (like finding and reading articles or writing parts of your proposal or dissertation) regularly (daily, if possible) that will move you forward (however incrementally) toward your goal.
This will keep your productivity high with the least amount of time and energy expended.
Like a good marathoner, expect to hit a rough patch once in a while, and predetermine that you will fight through it and keep moving, even if it feels like the proverbial wall (i.e., the 20-mile mark in the marathon). After all, as the saying goes, earning a doctorate is not easy or everyone would have one.
Finally, keep yourself motivated by imagining the sense of accomplishment you will feel, and the opportunities you will have that would otherwise not be available to you, when you cross the finish line.
To learn more about the challenges of the dissertation and how to overcome them, read Dissertation Research: An Integrative Approach.