Whether you use Roman numerals or bullet points, outlining is an effective way to capture the hierarchical relationships between ideas and data. In a history class, you might write the name of an important leader, and under it the key events that he or she was involved in. Under each of them, a short description. And so on. Outlining is a great way to take notes from books, because the author has usually organized the material in a fairly effective way, and you can go from start to end of a chapter and simply reproduce that structure in your notes.