Here's the secret: start early and start by spending a few days sketching out what objects/classes you will use and how these objects/classes will fit together. You are encouraged to discuss your ideas with classmates (but don't write any code together!) and to bring your design ideas to the TAs during office hours, or on the newsgroup, for comments/suggestions. The most successful students have spent time carefully planning their projects. Those students who do not devote any time to design are the one most likely to receive a poor grade.
Many of you have probably been able to sit down and do many of the projects in the lower level classes in an evening or two with little or no planning. Well the honeymoon is over. If you don't start early and spend time carefully planning each part, you will be very hard pressed to get a fully working solution. Good design and testing, not Mountain-Dew-Code-A-Thons the night before the due date, is the key to surviving 420.