1) find a system that works for you
-binder, accordion file, etc.
2) keep notes
-use a planner, sticky notes, etc.
3) have a notebook and folder, or section, for each class
-this way you can keep notes and work in one place
4) keep an area you always do you work and put everything you need there
-this could be pencils, paper, calendar, etc.
5) don't put EVERYTHING in your backpack, only the essentials
-this could be pencils, erasers, lead, and a stapler
6) find a study system
-flashcards, reading, writing everything over and over, etc.

NOTE: some people work better with music

Staying organized helps people get better grades. Find a system that works for you. Don't get lazy with it though! If your system requires you to rewrite your notes, DO IT!