You can take following steps:
1. You can secure your wireless router, you can do that by changing SSID of your network so that it is not easily guessed. For router security, prefer WPA2 or WPA if available over WEP. Use a firewall.
2. Keep you anti-virus software, web browser and operating system up-to-date.
3. Not just computers, protect smartphones, gaming systems and all other devices connected to internet.
4. When you use any external device like USB or a CD, DVD then scan it for viruses before using it.
5. Protect your money when you shop online by not saving passwords and check if the website address starts with https instead of just http.
6. Keep backing up your data regularly.