Tell him to keep his nose clean there is still lot of boozing, drugs
and loose sexual behavior on campuses which should be expected since
most Universities and their adjacent dooms are full of young
inexperienced and experimenting adolescents.
A preconceived self awareness to these facts can be a valuable acceptance while there.
Nonsense. Tell him to make responsible decisions about everything, including sex, use of drugs, and the kinds of people that he allows in his life, that includes religious people in campus that recruit for harmful organizations like the WT.
Instead of being narrow about sex is this, drugs are that, reinforce his self-love and self esteem, and that way he will be responsible in any decision he makes. Also make sure that he has good education about the problems that abuse of drugs cause, and the problems that irresponsible or risky sexual behavior can cause, some of them permanent.
FEAR doesn't work. Telling him "this is bad", doesn't work either. reinforcing being responsible with himself because he's worth it does wonders and he applies that principle to everything.
Regarding the educational college experience, I'll give the same advice my father gave me. It was one simple word: learn.