First of all, this only applies to Windows, I don't do anything special to Linux.
1st Step:
Software that you don't need.
Go to Add/Remove Software in the Control Panel and remove any firewall, antivirus, antispyware, anti-anything that you have installed
2nd Step:
Firewalls.
If you have a router firewall, take the time to learn how to configure it: ask question in forums, chat on IRC and read tutorials, it's not that difficult.
If you don't have a router firewall, then you'll have to try out different software firewalls; the less intrusive the better. Remember to choose a firewall that's only a firewall, if it has other features like blocking cookies, block sites, etc, DO NOT USE IT.
I recommend Prisma Firewall (http://www.prismafirewall.com/). ZoneAlarm and other similar firewalls are too intrusive and leak-able like any other software firewall out there.
3rd Step:
Protection and Surfing.
Install: Opera (http://www.opera.com/), Prevx1 (http://www.prevx.com/), and Netscape Browser (http://browser.netscape.com/ns8/).
Use Opera for Internet surfing, NEVER USE INTERNET EXPLORER. If you are paranoid, like me, from the Preferences window disable Java, Java script, plug-ins and cookies; if you need to use any of them you can activate them per site: if you want cookies and java script for forumophilia, you just go to the site and right-click and choose "Edit site preferences". You can also disable cache or set it to be erased when Opera exits., and never use Wand.
Prevx1 will be your antivirus/antispyware/anti-anything, you don't need anything else. Default configuration is good enough and recommended.
Netscape Browser, you can use it to surf the web if you want, though Opera is recommended, what we want is the antispyware program it includes. In the very rare case that a Trojan/spy-ware/virus reappears over and over again after being deleted by prevx1, just perform a full scan with Netscape's antispyware and it will kill it forever.
4th Step:
Updates.
Remember to update windows monthly, and to updates all the programs that you use the most. Setting prevx1 to check and update automatically is recommended. Also remember to update drivers.
5th Step:
System Maintenance and Privacy.
Delete traces, cookies, temporary files, cache, etc, with Privacy Guardian (http://www.pctools.com/privacy-guardian/). Configure it in accordance to your needs. Delete traces whenever you think its needed
Repair and clean Windows registry with Registry Mechanic (http://www.pctools.com/registry-mechanic/), set it to seek and repair all kinds of registry errors. Do it monthly or two time a month if you install and uninstall programs constantly.
Defrag you hard drive with Perfectdisk. Do it monthly. Click on "Analyze" and normally it will recommend a boot-time defrag, do it. After that, analyze again and it will recommend a SMART placement defrag, do it. Notice that boot-time defrag is only needed for the partition that boots up windows, commonly "C:\".
That's it.
Your Windows installation will become a decent OS.
