Step 1: Understand the question.
We must find the one thing a teacher should be most conscious about in order to teach well.
Step 2: Recall how teaching reaches the student.
A teacher may know a lot, but that knowledge helps no one until it is passed on clearly. The bridge that carries ideas from teacher to learner is communication.
Step 3: See why communication matters.
Good communication lets a teacher explain ideas simply, hold the students' attention, invite questions, and clear doubts. Without it, even deep knowledge stays locked inside the teacher.
Step 4: Check the other options.
Keeping the class obedient or pleasing the head teacher does not directly help learning. Reading many reference books builds the teacher's own knowledge, but that knowledge still needs to be communicated to be useful.
Step 5: Pick the strongest factor.
Among all the choices, only improving the ability to communicate works directly on how well students receive and understand the lesson.
Step 6: State the conclusion.
To be an effective teacher, one should focus on improving communication in the class.
\[ \boxed{\text{Improving the ability to communicate in the class}} \]