What is the most important thing to have for a new teacher when entering the class? Knowledge, Confidence, Impressive dress, please write only one.

I prefer Confidence. 

Can I cheat and say "confident in your dress and knowledge"!

I think that confidence includes knowledge and confidence.no one would be self confident without knowledge and being able to impress students.Luster of appearance will vanish if there is no knowledge or confidence.

knowledge

I think it's knowledge. A knowledgeable teacher is the one who is full of confidence and a confident teacher posseses beautiful personality.

genuine interest in teaching and positively influencing  the young minds! is what is most needed!!

the traits you have enumerated are a prerequisite though dressing to impress is rather superficial. dressing approapriately is needed! if one does not have a genuine interest in teaching, and welfare of students upportmost on the mind one cannot inculcate values of life in the student's mind. Selfless and unbiased behaviour  enables a good teacher to become a GURU ( Sanskrit origin made up of two parts GU meaning darkness and Ru The one who dispells ) the dispeller of ignorance and a true guide.