1. backup data regularly and image partitions if possible
And keep it on a completely external medium (ie.: an external USB drive or a CD-RW) and be sure to test that your backup is valid and also test the backup medium itself for structural damage. If your data is even more important to you, take your backup with you when you if on trips that are a day or more and/or seek out a remote-backup solution.
4. empty temporary spaces often, particularly when something seems a little odd, or you end up somewhere you didn't expect while browsing, and particularly before you reboot the computer
Some web browsers are capable of emptying some or all of the browsing information when closed. For example, Internet Explorer can be set to clear the cache every time it is closed and Firefox can be set to delete pre-selected browsing data (history, cache, cookies, etc.)
5. use as few browser plugins as possible and keep them updated as often as available
Note that "plugins" are not necessarily the same as "extensions" in Firefox.
6. keep up on all software updates when available (media players, office software, etc.)
However, it is sometimes good to wait just a couple of days (if, perhaps, it's not a critical update) to see if there are reports of problems with any specific patches. Otherwise, be sure to have a recent backup of your operating system as an image or partition.
7. use an email client that can be set to plain text email, preferably with no images inline, and where the email client does not have the ability to run code, period - and be careful with emails!
Some mailers, such as Eudora, include their own basic browsing engines which render only very simple formatting and images. If you must use HTML mail -- particularly in Windows -- these are generally much safer than letting the mailer use Internet Explorer's browsing engine.
That's right folks. Security is a myth. No matter how thick the walls in your bank vault are, there's always the chance that someone will have enough dynamite to bust it open. So, be on guard in order to close the biggest hole in your personal digital security: you!