Which ONE piece of advice would you give a teacher who wanted to create their own classroom material?

Which ONE piece of advice would you give a teacher who wanted to create their own classroom material?

One advice that I would like to give to a teacher, and to myself as well as a reminder, would be to always put yourself in the students' shoes. Always think whether they would benefit from the materials or not. Think about what the students want, remember them and try to differentiate between materials so that all students get a chance to be involved in the process.