- Don't install desktop software when there is a viable online alternative. Email is best served up as a web-based medium. Word processing, spreadsheets and presentations should be covered by Zoho or Google Docs. Even creating and maintaining your website could be moved into the cloud! Following this rule closely will free you from most constraints of choice in OS.
- Buy the smallest computer that can efficiently run the desktop software you require. If you are doing video rendering, or audio editing, then fine, buy what you know you need. But if you are just making a few websites and surfing the internet, you can buy the cheapest thing out there, secure in the knowledge that if it takes a complete dump, it's easily and cheaply replaceable.
- Buy and use an external drive for your documents. This will teach you the discipline of properly organizing your files onto that drive. It will also facilitate moving those documents from computer to computer with a minimum of fuss. If you use a portable computer, then your drive should be attached directly to your network. If you take this computer off-site but still need access to those files, you should either set up access through the internet, or syncronize them to a local directory on the computer.
- Backup your most important documents to TWO USB flash drives and store them in a very safe place. Flash memory appears to have a far, far longer lifespan than optical media (CD's or DVD's) and is much more portable and interchangeable. Netbooks and notebooks nowadays are beginning to appear without optical drives, but just about everything has at least one USB port. Included with this rule would be making a schedule for doing this, and then following it. As part of my month-end routine, I always copy all the previous month's pictures and videos to both drives, and store them in a fireproof safe in my basement.
Oh, and a possible fifth rule that really only applies if you are in a business environment, or providing IT for people, is that it would be best to backup computers by imaging the drive regularly. Do not just backup the files your client tells you are important. They have spent probably years getting it set up in a manner that no matter how inefficient it may seem to you, they know how to work with. An image will get them up and running with a minimum of callbacks to you.
Please, feel free to let me know if you have any of your own "rules", and I'd be happy to add them to the list if I felt they were listworthy :)