PC Magazine has a nice collection of tips (72 of them) for “Safer Computing”:
You might wonder if it’s even possible to have a safe computing experience in this day and age, beyond unplugging your broadband connection and never installing any software. Of course it’s possible, but it will take some work on your part. You need to install tools to protect yourself, learn good practices, and most important: Exercise common sense. Here’s what you need to do, from the bare minimum on up.