Organization

The ability to establish and maintain a system for arranging or keeping track of important items.

There are two keys to helping students be better organized. First, an organizational system needs to be put into place. Second, the student will need to be closely supervised for a period of time (probably longer than you think) in using that system.
Let's consider each of these strategies separately.

"Getting organized"
Organization systems

While the student with ADHD who has difficulties with organization, may need some individualized supports, a classroom with clear organization systems such as homework collection areas, student assigned areas, etc. can make a lot of difference.

There are a multitude of ideas on the internet for organizing a classroom. Rather than put the multitude of ideas into place (unless that's who you are as a teacher), consider hunting down specific ideas based on where students in the classroom are having difficulty.

For the student's personal organization system, involve the student in making choices. Help him choose a system that is easy to use for the student. It might be organizing work into separate binders, separate tabs within one binder or the use of folders rather than binders. Helping them organize electronic resources is also important. Baskets might be easier to use than folders.

Students put their clothespin on their work as they turn it in so that the teacher can easily see who has not turned in their work.

"Staying organized"
Supervision of the use of organizational systems

Once the system is in place, it is important to realize that the student will require frequent monitoring and assistance to keep the organization system going. This was covered on the "Big Ideas" page! Initially, setting up the system will be novel and the student may be enthusiastic but eventually, he'll find it tedious (because it's work to remember to use it) and it will become more difficult for him to engage with the organization routines.

Students with ADHD need to learn how to take other people's perspectives to see whether their "stuff" is organized or not. Sometimes taking a picture of what a space should look like is useful.

Teachers often put a rewards system in place ("If you turn in your work all week, there is a prize") but for students with ADHD, if there are no "point-of-performance" supports in place to actually help him turn in the work, the rewards will not be effective.

For upper grades, ask students to put their homework on the corner of their desks first thing upon entering. Then, go desk by desk, checking off that homework is done.