In my view, it is important to cultivate good habits in divers early on. Instructors use various techniques such as multiple repetitions of key concepts so that we cement certain behaviors and concepts in the students’ minds.
Part of being a good instructor is being a good role model. Often more is caught than taught in instructing students. Students carefully observe the instructor and will subconsciously adopt certain behaviors and habits from their entry level instructors. I remember thinking about how gracefully my entry level instructor moved through the water and it was my goal early on in my SCUBA diving to move as gracefully as he did. I can clearly remember how he instructed my class on how to set up the SCUBA gear. I still use the same method and teach it to my students.
Even though the most important rule in SCUBA is never hold your breath, for instructors, the most important rules could be to always be a good role model and help instill good habits in your students.