Let me preface this post with a small disclaimer. I'm not a neat freak. I keep my apartment organized because it helps me prevent unnecessary anxiety, but I'm not one to write every detail of everything down. This is just a collection of the ways I stay organized in the hopes of being fairly successful in school.
I have begun using an agenda. This is fairly new for me. In elementary and middle school when they were mandatory, I'd make fun of the corny designs and inspirational quotes, then it would collect dust on my desk at home, unused and sad. In high school I wrote my assignments on my hand and hoped for the best (model student, I know.) If something was really important, I added in the calendar on my phone, but I never remembered to go back and check. In my first years of college I got better at writing down my assignments, but never in an agenda. I usually just made a notation at the bottom of a page of notes, but that was only effective if I remembered to go back and look.
This past summer I bought a nice agenda to keep track of my ever-changing work hours and to keep track of what I was writing for Bruised Knuckles. It was surprisingly effective. Yeah, yeah, I know I should have tried this years ago. I'm not anal about what I write down, but the layout of this Moleskine agenda is extremely helpful for me and meshes with what I find natural. One side has a block for each day of the week and the other is lined for to-do lists or notes.
I like to write down what classes I have that day and if a larger assignment is due. I also write down what's assigned for homework and any tasks I need to accomplish that day. I use transparent and opaque post-its to mark especially important things to draw my eye to them, but there isn't really a color coded system.
I primarily take notes with paper and pen, not on a laptop. I use the binder notebook hybrids by Mead or Five Star so I can clip in handouts, or put them in the folders, and take notes on the lined paper. I separate them by day of the week, so I have one for my Monday/Friday class, then another for my Tuesday/Thursday classes. I then separate each section with the provided poly folders so I don't get any of my classes mixed. I don't use any method of note taking, but I do date each new day of notes for reference later. I'll highlight key terms in yellow, and underline stuff that seems important so it's easier to study later. It's a fairly straightforward method, but it works for me.
I prefer paper textbooks to digital ones and buy mine off Amazon used to find the cheapest price. All the English classes I've taken have conditioned me into annotating as I read, so I do mark up my books. I often make notes in the margins and underline and highlight important parts. This makes skimming for exams much easier, but may not be allowed if you rent your books. Check to make sure before writing in them, or if you don't want to worry, buy them used, then sell them later on.
If there's something I need to remember, I'm likely to write it on a bright Post-it and stick it to my wall, desk, closet door, or TV. They're in places I commonly look so I don't forget, but they're easily removable.
I like to keep the desktop screen of my computer very neat, just for my own sanity. I keep three folders. School, Work, and my hard drive. I have those subdivided into each of my classes and each of my work projects, and every couple of days I take everything that built up on my desktop and sort it into the respective folders. I also take this time to back up all my new files on an external hard drive, Google Drive, and/or the flash drive I keep on my keys (something I'd highly suggest to everyone to try.)
My Android recently completely died on me, so I'm back to the Apple ecosystem. My laptop, iPad, and phone's calendars are all integrated so I get notifications and reminders on whatever device I happen to be using. Android's Google Now launcher is comparable, when used along with the Google Calendar and Inbox apps. I do prefer the Apple ecosystem, though,
I also have a hanging month calendar on my wall, which I use exclusively to X out days. Inefficient, maybe, but it holds an odd sense of satisfaction for me.