You need the before principle. Aside from that, there's no difference in meaning between the two sentences. The second is just a short version of "I'm going to be a responsible student and follow the rules that have been set out by the principal." (passive voice)
These are exactly the same meaning. #1 uses present perfect tense, active voice in a subordinate clause. #2 uses passive voice in a reduced clause.
"I'm going to be a responsible student and follow the rules the principal has set out." "I'm going to be a responsible student and follow the rules set out by the principal."