A common mistake made by students writing dissertations is to stick with a supervisor who isn't the right fit. While ideally a supervisor should be an expert of the dissertation topic, it is more important that he or she be reliable, supportive and able to give detailed feedback. Particularly early in the process, it is advisable to swap to someone who can act as a lifeline rather than toughing it out with a supervisor who is unavailable.
Expect to panic at least a few times during the process. The majority of students get paranoid about their topics and decide to start something new at least once. Most of the time, this is just the result of nerves, and there is no real reason to start over.
The majority of dissertations involve a significant amount of work that doesn't make it into the final revision. Editing content down to be as clear and concise as possible is important. Don't get too attached to any particular ideas, especially early on.
Format can be a major source of worry while writing a dissertation. Furthermore, finding the right format can make creating content easier. Consider visiting the university library for examples and further instructions on how to write dissertations properly.