Answer:
Probably just enforcing it little by little. (If you mean a habit. If you mean a certain topic it's different.)
Step-by-step explanation:
If you are trying to teach your students a habit-
Try to correct them everytime they don't follow it. Expect them to do so and give a reward when they earn it.
If you mean a certain topic-
Make a slideshow or a presentation with an interactive game. Making it not boring and having them more attentive.
I gave a more general answer, so if you would like to go deeper into the subject I would be more happy to.
(If this helped, please let me know. If you have any questions do not be afriad to ask!)