Machines & Software
Make sure all software is up to date (see Standard toolkit).
Install Anti-Virus software (see Standard toolkit).
Don't click on any Web, instant messenger or email links that were unsolicited, even if it looks like it has come from a friend.
Be careful who you give your personally identifiable information to, i.e. market researchers etc (remember, ask for ID) as they may be able to use your details online.
Use encryption on hard drives if available. MACs have FileVault and Windows 10 has BitLocker.
Routers & wi-fi.
Always change default passwords, especially on routers.
Change the SSID (Service Set IDentifier) on Wi-Fi routers. And use a name that will not identfiy you.
Set the WiFI routers security options to the highest possible level. WPA is better than WEP.
The best Encryption methods to use for wireless are WPA2 and AES.
Use random characters for the PSK (Pre Shared Key) on your wireless router. You can always cut and paste.
Do not use anyone else's Wi-Fi without permission as it is both illegal and exposing yourself to security risks.
Always secure your Wi-Fi network to stop others "piggybacking" as this will also expose you to security risks and will slow down your bandwidth. Fraudulent operations done though your router will appear to have come from you.