My tips for healthy computing:
1: Backups. Fundamental
Whether it's the program that came with an external drive or a secondary disk with some free backup program. Always have backups of your personal data.
2: Antivirus. Stop clicking on things.
If you are a veteran computer user you can get away with free antivirus and stay perfectly clean. AVG Free and Microsoft Security Essentials are the top two I swear by.
No need for software firewall programs unless you have some strange paranoia. Consumer level routers are more than enough.
Do not install more than one active AntiVirus. In fact stick to AVG/MSE, a router and your intuition. This will allow your machine to run at peak performance. Don't be lazy and install a bunch of 'security' applications thinking they will just magically meld together into a super anti-AIDS wall.
3: Hard Drive Health: 'It is not a question of IF a hard drive will fail, but WHEN'
Hard drives fail. If you notice any slowness, crashing, BSODs, application hanging, problems booting... check your hard drive for signs of failure. SMART data will record main points of failure: Sector damage. Pending and Reallocated Sectors are critical signs to clone out the drive ASAP.
4: Updates: Duh!
Keep your OS and software up to date. This will help prevent bugs/crashes as well as security threats.
5: Maintence: Ccleaner, Defragmentation, Case Dusting & Unwanted programs
-Ccleaner will boost computer performance IF and only if you have an older machine (and not cleared temp stores and whatnot). Do a system scan for temp crap every few months, as well as the registry scanner built in.
-Defragmenting once a year will reduce stress on the hard disk, do it. Plus you'll get a slight performance boost with certain operations.
-Case Dusting lowers heat, lower heat = less stress = better performance / longer life. I go with a ShotVac and blow the crap out of the case. Vacuum is not very effective. Go with something a handheld blower or a shotvac

.
-Don't install a ton of shit. Clutter is your enemy. Remove old unused programs. Try to keep your system tray under 30 items.
6: Intuition: Caution
Just be careful where you're going and what your clicking on. That in itself will prevent 99% of all virus related downfalls. Like I mentioned before - Free AntiVirus is plenty if you know what your doing.
This information will keep your machine performing like a 18 year old girlfriend. Keep things simple and efficient!
Side notes
Registry: Dont touch it
People who know nothing about the inner workings of Windows will share with everyone else the ominious lurking pitfalls of a corrupted registry and how it needs constant cleaning and optimizing. And you wonder why they are always asking if you know what error 0x000000XX means.