There are some definitive criteria like passing all the Plebe Knowledge Tests, conducting spirit missions, etc., but there are also some subjective ones. General class participation in following the plebe rules for example. It is actually very noticible if a fair number of plebes no longer square their corners, or walk in the middle of the hall. Even those who are ambivalent towards the regimental system will get annoyed and let the Reg. Officers know.
I also advise not getting caught up in trying to be a class leader as a plebe. A surprisingly large number of them don't seem to graduate and it will have about 0% impact on you getting into the USCG.
"Lo Pro", as in Low Profile is the way to go as a plebe in my opinion. Grades, grades, grades!!! There will be plenty of time to fully immerse yourself in the regimental system as you progress through further years.