i know you dont know the principal of my school but i just need some ideas, especially on the type of language part.
In general, the principal would need to sound like a well-educated man who tries to be a good example for his students. This means that he should use high-level vocabulary and he should not, in general, use slang terms. He will also be pretty likely to speak in longish sentences that have many clauses too them. In other words, he will speak more like someone writing an essay than like some teenager just talking.
As far as what the principal would say, you should keep in mind that he would be most concerned with wanting people to do the right things. This will influence the sorts of thoughts he should have. He should not be all happy, for example, if someone mouths off to a teacher.
I think the type of language he might or might not use would depend upon the situation in which it was being used. If he was telling a story about a student who had just won an award for outstanding academic achievement, his language would be filled with adjectives describing the hard work and long hours the student had maintained. If he was talking about a student who has dropped out of school, the language would use a vocabulary reflecting disappointment and possibly frustration with the student or the circumstances that the student to leave school. In all cases, I would hope the principal's language would include grammatically correct sentences using terminology reflecting his degree of education.