Writing your dissertation is a long drawn job. To start with, it may seem like a huge burden. But as you get writing a few chapters your confidence will surely build up, and you will start enjoying your work. This is all true if you take the right approach toward dissertation writing.
When you start with your dissertation, you would be spending a lot of time reading literature relevant to your research. Ensure that you read only the right stuff and not spend time reading unnecessary topics. You could be in constant touch with your supervisor to ensure that you are on the right track.
In the middle of research it is natural to get bored and insecure. You might even feel like giving up the idea of pursuing a PhD. If you feel so, you need to find the source of problems. Then take concrete steps to resolve them. It is important that you break down your total research into smaller milestones. A small milestone will seem easier to achieve than a large total view.
You could also discuss the progress of your research with colleagues and friends. This could provide you with some positive feedback. Thus maintaining a positive attitude and remaining motivated will go a long way in accomplishing success in dissertation writing.