I usually tell them the following:
- Enable WPA and MAC filtering on their home router. Additionally, change the default password and disable remote administration (not needed in most cases).
- Download and update a free malware and/or spyware scanner (MSE)
- Consider attachments from anyone potential threats because that person's system might be hijacked
- Use a keychain to secure their passwords (KeepassX) whenever possible. It's good to explain how to care for this secure password storage file and keep it backed up.
- Make regular backups of important data in at least two ways (storage media and dropbox)
- Regularly update the OS and Software they use. A tool like Secunia or AppFresh (For Mac) can usually make this a lot easier.
- Use a PDF reader that isn't from Adobe.
- Try to show them how to get software they need from better locations and how to do basic research on problems.
- Try explaining to them why they should pay attention to messages that are generated from the OS and software before simply trying to click their way out of it as fast as possible.
- Point them to resources on being protected against Identity theft.
- Give them a basic overview of what makes a good password and changing them every so often.
This is all I can think of off the top of my head. Hope it helps