I go along with Microsoft Security Essentials and Spybot S&D in Windows 7, with CCleaner every now and then, mostly to clear temp files.
There are excellent software tools, but security to me is more a matter of mindset. From the top of my mind, a few points people usually don't care about:
Always install security updates to all the software you use, at least for those that connect to the internet.
Don't install pirated software, and read the screens in the install process to prevent random browser bars and "add-ons" to be installed. Even better, try to use portable software whenever possible, to avoid polluting the system.
Have a good router with some basic firewall capabilities.
Don't connect to untrusted wi-fi networks, and if you must, use a VPN and avoid doing banking or other sensitive activities.
Don't plug USB devices that have touched other machines, unless they have a read-only switch and you know it has been used :)
Use adblock, and if you have the patience, script/cookie/request blockers
If you go around joining random wi-fi networks, using usb devices from random machines (even if the owner of the usb stick has the best antivirus ever), and letting flash adds load freely, you'll have a bad time.
Of course, you can be the most careful person ever, and you may still have open vulnerabilities in your systems, that is the kind of weakness software tools should be used for.
Just my 2 cents...
1This is a discussion topic, not a specific, answerable question, and not really suitable for this particular site. – David Schwartz – 2015-12-01T20:05:53.780