I think we all know what positive language should sound like, but actually getting it into your daily routine may be a little more difficult. To begin, it's essential to know that your thoughts shouldn't always match your verbal output. In fact, it's pretty unhealthy in the classroom to have a teacher who responds emotionally and perhaps in a verbally uncontrolled manner - it's a quick way to build resentment and demolish all the chances of having those very important relationships built on trust and respect from both sides.
Positive language takes time to develop - one phrase, one strategy at a time. It's a little like learning a foreign language. Little, by little, build your vocabulary of words, gestures, style and phrases that elicit a positive response from the children. Everyone will end up much happier because you undertook perhaps the most important piece of professional development you will ever do. It's really important to have others who can mentor you and suggest successful phrases they have used when dealing with the daily barrage of sometimes unwanted oppositional language from the students, choose them carefully