What teachers need to make sure students know. Do not 'assume' they already know it.
Know the difference between personal and private information.

Go beyond Internet Safety
http://www.commonsensemedia.org/educators
Example: Keep it Private
http://www.commonsensemedia.org
/educators/lesson/keep-it-private-2-3
Very simple rules for young kids, but take a look at the lessons as you get to middle school
http://www.commonsensemedia.org/
educators/browse?grade%5B%5D=4826
1&topic%5B%5D=48236&type=
csm_curriculum_lesson

Older students should be able check their understanding through peer discussion. Here is a good presentation[  get_fileinternet.pdf ] by Karl Hopwood which can be used with that age group.

Downloadable Poster from Edmodo - Best Practices for Digital Citizenship

Creating Avatars
Some schools ask students NOT to use their real name. If you need to help students create avatars, here are a few sites. Yes, there are other sites, but these are both fun and safe, and quick as time is precious!

Build your Wild Self
http://www.buildyourwildself.com/
New York Zoos and Aquarium let you create a 'person' with animal parts.

Digibody
http://digibody.com/avatar-maker/index.php
Create an avatar from facial parts and expressions. Good for the slightly older student.

Dopple Me
http://www.doppelme.com/
Create a cartoon character.

Clay Yourself
http://www.clayyourself.com/
Build a clay model of yourself.