Hmm... what I mean by that is at the very least encouraging students to do more social service/community service.
A little curious, at your school what do you talk about at assemblies?
I guess I better defend my school here:
Uhh, upcoming events (school productions, music nights, exams etc.), achievements of students/staff (usually sports, debating etc.), reinforcement of rules (littering and uniform, which has been cracked down on hard; not hanging around in groups at the local shops also a big point [i think the local shopkeepers were getting annoyed]), stuff about taking advantage of opportunity and studying hard, new plans for the school etc. Also usually have a student band/soloist play some music.
I guess the littering thing is an example of bad values, but the amount of rubbish on the ground has reduced greatly since they started cracking down hard on it.
If you want recent examples of helping out the wider community, there's some students at my school that organised some overseas trip over the holidays to help out people in need there. Also there was a fundraiser that's being going on for a while to send a group of students to go to Northern Territory and spend some time helping people there (I think they've managed to raise enough money for that now). That stuff will get mentioned heavily at assemblies as well.