Protect yourself on the Internet

1. Have at least 4 e-mail accounts for 4 purposes: 1 for official e-mail exchange with known people, 1 for important social community (Facebook, chat, blogs, photos, forums), 1 for importantfinancial purpose (online shopping, online banking), 1 for not-important communities & activities (forums, ads, newsletters). All e-mail accounts should have backup e-mails, phone numbers, security questions. If you lost 1 account you won't lose everything.
2. DO NOT share your account with other person if not necessary.
3. Have 1 Antivirus and Firewall software installed & latest updated on your PC. There are some kinds: Antivirus, Firewall, Antivirus + Firewall = Internet Security or Total Security.
4. Latest updated OS, Internet browsers, E-mail clients.
5. Backup important data (e-mails, documents, blog posts...) regularly & store safely.
6. Use HTTPS instead of HTTP when sign in if the website supports.
7. Consider carefully the content of e-mail, instant messages, web pages... if you're not sure it's safe, well-meaning or related to you, just ignore or delete it. 
8. Don't be greedy to very easy big and valuable offers (it seems unreal) or anything else like lottery, luckiness or money transfer if you didn't request.
9. Always check URLs behind URLs shown at your eyes in e-mail, instant messengers or others by moving mouse over URL to view the real URL on Status bar of the browser before clicking. Do not click on URLs that you don't know well.
10. Always check the spelling of URLs when you type on Address bar of the browser. If misspelling may lead you to fake website for stealing your personal information.
11. Always download software (especially FREE software) from reliable download sites to prevent virus, trojan, adware, keylogger attached with software.
12. For important accounts: Do not accept the browser to remember your passwords or form fields.
13. For important accounts: To prevent key logger, use virtual keyboard to enter information. Windows 7 has utitlity On-Screen Keyboard (Win+R > type "osk" > Enter).
14. On public PC & public wifi: NEVER REMEMBER Passwords. ALWAYS CLEAR Browser history (temporary internet files/cache files, cookies, forms, passwords...) and Recent Documents after using. Because most of public PCs always have viruses + key loggers, you must be so careful.
15. Clear recent history and forms regularly to prevent hacks or after important surfing. Use private browsing when needed.
16. Do not upload your nude/sensitive photos to anywhere else on the Internet.
17. Consider carefully which photos/videos/info will be uploaded to the Internet. Choose appropriate sharing mode (private, limited with link, friends only, public...) for your photos/videos/info to protect yourself from stealing or misusing.
18. Do not expose your real personal information (full address, official phone number, full name, birthdate...) to public. Share it with limited ones when necessary. You can use a not-important phone number for public transactions.
19. Categorize your friend list (families, well-known friends, not-known friends) and set appropriate privacy settings for those. Share your personal information with your families & well-known friends and limited personal information with others.
20. Take care of the information/speech you expose to public because it may hurt you in the future or some employers may search your online profile to consider your job. A (true) good image of you will be a plus.
21. Always update security info and improve your security awareness to protect yourself.