The students need to take responsibility for their actions online; make sure that they are visiting appropriate websites that are safe not only for them to use, but also safe for the technology itself (i.e. don't go to unknown websites that could simply be havens for viruses). They need to know when they are allowed to check email using school property that they should not open attachments that they don't know anything about.
2. Following the law
Students need to know what they can legally use in their presentations and documents. In other words, they need to be aware of fair usage laws and how it applies. (most of them probably think nothing of using one of their favorite songs as a background music for a presentation, but don't realize that when they do that, they could be violating copyright laws.
The rise in usage of texting and instant messaging in current generation (i read somewhere its called the millennium generation) has inversely led to a decrease in professionalism as far as writing skills and presentations. Its amazing that students will hand in final drafts of work that have numerous spelling and grammar errors; they will use short-hand, or code, in school papers that they use online because they think that is how it is done everyone. I see their point, since that is all they know. However, they need to be aware that there is a higher level of professionalism expected.
Thusly, I would teach digital citizenship with a focus on the above three; before being aloud to get online, they will be made aware of what they can/can't do online, and that we aren't just getting online to "play." They will get a lesson on copyright and fair usage law and how it applies to them. They will also be held to higher standards as far as what/how they write their material; i plan to use a class blog to get them to practice and improve on their writing skills.