What you need first is a calendar. You could buy a nice one at the bookstore, or you could get a free one just by clicking on the link above. It's not fancy, but it's free, and it's got all the important dates on it.
Then you need 4 colored highlighters, each of a different color. Colored pencils would work too. So might crayons.
You need all of your syllabi.
Got everything?
1. Transfer all of your big due dates onto the calendar. Tests, quizzes, papers, responses to reading, lab reports... . For the whole semester. August to December or January through May. Right through exam week.
2. Color-code each class. Econ green, for instance. Bio blue. Pick colors that work for you. Highlight each assignment in its new color. (If you use colored pencils, you could write the courses in color. For crayons or markers, underline in color.)
3. Estimate how long an assignment will take. Draw a line backward in that course's color to the day you'll need to begin that assignment. Repeat for each assignment. (Example: say you've got an econ exam on September 28. You decided you need to start reviewing a week before. Draw a green line backward through the week and into the previous week to the 21st.) Your Syllabus Map should look like this.
4. Two colored lines in one week? Remember, there's a limited amount of time in a day. (If you haven't figured out yet exactly how limited, go to the 24-Hour Weekly Planner.) You'll need to draw those lines further back. If any lines overlap at all, draw them both at least a day further back. If they overlap a lot, consider doubling the length of each.
Colorful schedule? In weeks with more than one color, you won't have time for much but schoolwork. In colorless weeks, you can ease up.