There are lots of fantastic note-taking apps and services out there, but I must admit, I'm more of a pen and paper kind of guy. This trick to organising your paper notebook is simple, efficient, and only requires your writing utensil.
Photo by Adam Akhtar
Adam Akhtar describes the process on his blog Highfive, and says he discovered the tip while in Japan. The set up is simple, but works very well. Take your empty notebook and pick a page to be your "table of contents", or list of how you plan to categorize your notebook's sections. Akhtar makes his categories page the very last page, but I don't see why you couldn't use the first page if you'd rather do that.
List out your categories, each one on their own line. Whenever you fill a new page in your notebook, mark the page by darkening the furthest edge of the paper on the same line that your category is listed on. Now you should be able to see what pages are in what category just by looking at your table of contents and the edge of pages in your notebook. Flip through your handy notebook and find exactly what you're looking for in no time.
If you want your notebook to be better for scheduled productivity and organised for time, check out the bullet journal method.