Tell students what qualifies as an exception to a rule or procedure. Tell them the length of papers, how they will be prepared, word count, and all other criteria. Overall, the goal of your syllabus is to inform students of the nature of the course, lay out your expectations, and form a contract between you and them. Instructors should make every effort to stick to the syllabus, especially the schedule, homework dates, and test dates. Any changes should be announced well in advance and put in writing.
Students like and appreciate a complete and accurate syllabus.
They feel more secure in knowing what is expected of them. You also protect yourself if you spell out exactly what you want from students. Another great thing about a well constructed syllabus is that you can transfer it to other courses easily.