I work as a project manager so organization is key to my success in my role. My advice would seek out and talk to people who you see as organized- ask what they do to maintain that organization. You can try out any suggestions, keep the ones that work for you and discard the others.
In my work role, I use project management software to keep all my projects and detailed tasks and documentation organized. There are a lot of free, and useful project management programs available on the internet. I recently used one of those free programs when my daughter was preparing for college her junior and senior year of high school. We put all the tasks she had to do, assigned them dates, built out a calendar and reminders. This kept her on task and focused on what she needed to do to get in to the college of her choice.