If we are talking about security in www, you should be aware of phishing attacks, you NEED to be always aware is your connections is secure. HTTPS should be used always There are many add-ons for each of available browser which will forcefully redirect you to https version of site you visit.
- Never reuse same password in multiple registration forms.
- Turn off auto-fill for pages if you have stored at least 1 time your credit/debit card number. There has been incidents where there are hidden fields to gather those codes.
- You should schedule an time interval when you change passwords on all sites.
Excellent advise for password creation -
https://xkcd.com/936/