Do use a surge protector. Panamax or APC is recommended
Don't use extension cords on the main power supply (where the power cable goes into the back of the computer).
Do Windows Updates until you have no Critical Updates left.
Do use antivirus software if you're using the internet. Do keep it updated.
Don't let just anyone come play with your computer.
Don't ever follow instructions in an e-mail that tells you to go do an update or "Try this game," etc., because the majority of the time it will be something that will cause you major problems.
Do back up your important files, often.
Do learn how to uninstall programs correctly, if you feel like there will be sometime that you want to remove some.
Do become familiar with what adware and spyware can do to your machine. This site tells you more.
Don't expect a technician to tutor you, that's a separate process from technical support. Do practice, read instructions, and use the Help feature that is available in most any commercial software. There is a lot of important information there.
Don't upgrade just to have the latest thing. Read product reviews first and ask around. Do check to see if you really need it.
Do be familiar with your computer's specifications. They will be an indicator of what type of software and hardware will be compatible with it.
Do not install any program on your computer, no matter how enticing the marketing technique, until you have done proper research on it.
Do visit discussion forums, where the experience of many people is very valuable. This one for example: www.windowsquest.com