First of all 21st century teachers must know technology, because of the developing technology there are some technologies used not only for teaching but to communicate and to know well their students. Try new ways in teaching such as teaching using the internet, social media, etc. And a 21st century teaching must keep learning because of what I’ve said before technology is developing, the teacher must be ready to learn about the trends and new technology so that they will be able to use and apply it to their teaching.
(Some photos are not mine. These are used for educational purposes only.)