7 Horrible mistakes you're making with Windows

1. You have too many files on your hard drive: Windows needs at least 15% of free disk space available for system maintenance. So, if your PC starts acting up, you may want to check your hard drive usage, before it's too late.
2. You don't use any firewalls: It's well known that Windows systems have several vulnerabilities, and surfing the Internet without a firewall is like leaving your car keys in the ignition. Don't complaint if somebody messes up with it later. If you don't like Windows Firewall, you can use third-party tools but PLEASE get one. 
3. You're gullible: The worst mistake you can do with Windows, because there are lots of infection sources and computer criminals.
4. You don't keep your security software updated and/or handle P2P, warez and the like: I won't start a crusade against software piracy here, because who follows me already knows what I think about it (this blog doesn't support any piracy). If running a system with outdated virus definitions is already a suicidal attempt, and so is installing pirated software, running pirated software without updating your security software means an almost guaranteed infection, so good luck with that!
5. You use a bunch of toolbars: Like I've already mentioned (Internet toolbars - a big hassle or a plus?), toolbars can come in handy, but some of them are particularly pesky, because they alter the default internet settings and fill your computer with crapware or malware. Stay away from them as most as possible. 
6. You install and uninstall lots of programs: That's just the worst thing you can do with a Windows system, because it messes up your OS and creates lots of orphaned entries, which can cause your computer to slow down and crash. If you just can't help testing software, like me, use virtualization solutions such as Sandboxie (see Sandboxie - free the explorer in you for more details) or Deepfreeze, so you can test any software without compromising or changing your system configuration
7. You've resigned to a poor performance: You've given up and think there's nothing you can do by now. You can improve your hardware, adding RAM or installing an SSD but you should rethink your habits in the first place and there are many steps you can take on the software end to improve your situation, like I've already explained in How to maintain and speed up your computer - an out of the box guide (computer surge blues), part 1 , part2 and part 3.