Decide what information and what date range you'd like to include in the timeline. You could organize it according to major discoveries, major movements in the discipline, major publications or all of these.
List all of the events that you'd like to include in your psychological timeline within the timeframe you've selected. You don't need to arrange them in chronological order at this point.
Research the events you listed and note the details of each event and the date each occurred. Consult books, such as History of Psychology, The Story of Psychology and A Brief History of Modern Psychology. Consult credible online resources, such as Learner.org and others. Remember to cite all of the resources you used.
List the events and their details in chronological order.
Draw a timeline across a page or on your word processor that is divided into the same number of segments as the events you listed in Step 4.
Write the date for an event above each segment on the line and the description of the event directly below it underneath the line. For spacing purposes, you may find that you need to create a number of lines if they all don't fit horizontally across your page. Conversely, you could remove some events and only include the ones that you deem absolutely necessary, such as the major discoveries in psychology.