What is the most important thing for teachers in classroom?

First understand the Students in your class... their wave length... their strength and weekness related to the subjects... so that you can help them to improve... and make them able for the society .... 

learners.Is learning taking place?

Actually teaching needs multifaceted attention at the moment a teacher enters in the class. You can't prefer one thing on the other. 

However, tailoring the answer in accordance with this question, I would like to say that a teacher should be with a mind-set of teaching while in the class.

Attracting the attention of students towards learning is the most important thing to do......

The most important thing for a teacher in a classroom is to develop a relationship of trust and love with their students and  to be comfortable in his or her classroom enviroment. If a student is comfortable with the teacher then they will naturally want to please them and if they are comfortable in their enviroment then they are more open to learning opportunities.

If the teacher is excited about teaching the students, then naturally the students will be excited about learning.

To make the lesson interesting and have the students participate in everything you are showing / I see,I do,I understand ,a system I have used on a number of occasions . It is very effective in the training of staff .The information retention rate is very impressive.

ability of mind reading or psycology.

Have an objective and communicate that objective clearly to the students.