Your dissertation should be about something you enjoy. Pick a topic that you like, one that you know you can write about for a long period of time. This is important because if the topic is not very appealing to you then you will lose interest in it and have to start over. So save yourself some revising work by picking a topic you are familiar with and like, a topic that will motivate you in exploring it in more detail than you have previously and bring some new aspects of it to light.
Know where and when you work the best. Sometimes the mind is more productive at different times of the day and in the right work spot. Find when you can write without having to force the words out, and find the place where you will be able to work the most productively. Usually some people find that they need a quiet place to work, others need a comfortable level of background noise to keep them focused, whatever your preference you will find it.
Do not let your dissertation be as dry as a bone. Just because it is a dissertation does not mean that it has to be without humor or wit. Anything lacking life can be quite a bore to read and you do not want that to happen to your dissertation. Do not go overboard with the humor, but instead find a comfortable balance between seriousness and humor to use in your dissertation.
When your mind gets stuck it means you have to move. Most people cannot work on one thing straight through without a break and when you hit writer’s block it is a sure sign that you need a breather. Pick up a book not related to your dissertation and go to a comfortable spot, say a coffee shop, to read it and not think about your workload for a while. Perhaps you need to go for a walk or do some other physical activity in order to give your brain a break and let it recharge.