A strong psychology dissertation usually starts with a narrow research problem, not a broad topic. Begin by identifying the population, construct, setting, and outcome you want to study. From there, shape the problem statement, research questions, and method so each section supports the same central aim.
Start with the research fit
Your topic should connect to available literature, ethical access to participants or data, and a method you can realistically complete. Before drafting chapters, list your core variables, likely measures, expected sample, and analysis plan.
Build the chapter map
Use the introduction to define the problem, the literature review to show the gap, the methodology chapter to explain how the gap will be studied, and the results and discussion chapters to connect findings back to the questions.