Self organisation is a big one here too. They go from being told this and that to being told go find out about this and that. They get a timetable and a planner - make sure they get to know them and use them religiously.
Homework tends to have some different rules attached to it than at primary - make sure you know them - e.g.
if you miss homework because you didn't write it down, it is YOUR fault - no one else's
if you miss homework because you were off sick and did not catch up through classmates it is still your fault - you need to be prepared for the next lesson - even if you were not at the last one .
Make sure you (as a parent) know the detention process - at ours detention can be given at any time - for any infraction - they will not necessarily let parents know that detention is being given - the first you hear can be that they need picking up at 4pm on Friday because they have had 30min detention and therefore missed the only bus.
(somewhat inconvenient when I don't drive, can't afford a taxi and school is 6 miles away - but hey-ho, detention is supposed to "hurt", and it has only happened once - so I guess it worked)
there are many more choices and freedoms given which often they are not prepared for - even little things can phase them at first - DD wanted to go to film club on a Friday - but it clashed with junior choir - she had to choose. caused much angst and "why can't they do them on different days?" etc - they need to learn to choose because life is like that....