You need to showcase the relevance and importance of the topic. You have to explain why the topic is important for you and for the entire fraternity of your subject. There should be a future scope of work in this field. The reader should go through the dissertation and find it attractive enough. There should be some loose ends from where some new dissertation topics can be started. If you want, you can start a new dissertation from the end of your existing dissertation paper as well. You can take help with dissertation if you want.