Hello Yash,

Under the Classroom Improvement Scheme (CIS) students can appear for improvement exams twice, once in October and again in February - March if they are not satisfied with their October marks. 

As for rules, there are no new rules, just the standard ones that you follow for the HSC exam. A new admit card will be issued to you which you must carry to the examiantion hall, it contains all your details including the subjects you are appearing in and their codes. There are no seperate rules for improvement exam candidates.