Strictness is very hit-or-miss at Montclair. While the University claims to be extremely strict about alcohol and drug use on campus, the punishments are dealt out without much rhyme or reason. One student could be removed from housing after being caught under the influence, while another will continue to live on campus after being found with a significant amount of marijuana. Overall, the safest way to avoid getting caught is not to break the rules on campus or at least keep it quiet. The Resident Advisors are also very different in their attitudes toward rule-breaking. Some don't care as long as you are not causing a disturbance, a few will let only their friends off, and others will bust students every chance they get. However, if someone is causing a disturbance and alcohol is involved, the police often get involved—and that will normally involve arrests, or at the least formal write-ups.
Dorm visitation policies are fairly lax and easily avoided, as long as you don't make a point of being rude to the desk attendant or causing problems. As far as class attendance goes, there is a University-wide suggestion that students shouldn’t have more than three unexcused absences, but professors vary widely in their personal policies. For example, some will fail you if you miss more than three classes for any reason, while others won't require you to come to class at all. Always check your syllabus or ask your professor. Other rules exist, but generally if you aren't breaking the law, you aren't going to get in any serious trouble here.