Proper notebooks, or weekly planners. Insist that students use a three-ring binder for all subjects, with enough dividers to separate the subjects and clear plastic pockets to hold items like pens and pencils. Set up proper work environment. Students need a quiet work space because most of them are easily distracted. It's a distraction whether they realize it or not.
Adequate lighting is also important.
Most children cannot work for more than 20 minutes at a stretch and still operate at top performance levels. Be aware of conflicts. Don't schedule homework time against the child's favorite television show or extracurricular activity. Stick to the schedule. If homework time becomes too flexible, then the schedule has no meaning.