A common mistake, particularly among beginning teachers, is to assign too much homework. It can be hard to resist doing so if parents push for more homework and assume that the best teachers assign the most homework. (This is not necessarily the case.) Most often, however, a math teacher can tell after checking five algebraic equations whether students have mastered the necessary concepts.
Teachers also need to coordinate their homework assignments with those of other teachers so that students aren't getting four assignments on a Tuesday night, but no assignments on Wednesday night. This coordination most often requires leadership and support from the principal or other administrator.
Finally, teachers need to keep alert to how long students take to complete assignments. It is natural in a class full of varied students for some to take longer than others. Moreover, it is fine that some students do take longer, since research shows that students with low test scores who spend substantial time on homework get grades as good as students with more ability who spend less time. If an assignment takes too long, however, this may signal that a student needs more instruction to complete it successfully.