There are a lot of guidelines that you can study from online sources for writing your dissertations. There are also specific websites that are devoted to providing useful information for writing a superior Psychology dissertation. You have to recognize how important this project is to you. You do not want to take any risk. If you keep in touch with your adviser, then you are going to be sure that whatever you are doing is appropriate.
However, if that is what you need, you can most surely find that easily with the help of you adviser. You can be provided a sample psychology dissertation then you can see what type of subject would work the most excellently, what kind of research methodologies would be the greatest suitable for a dissertation on psychology, and you can see what type of material should be included in your literature review.