Cami seems to have hit all the high points. And I can't really add too much more for the residential machines.
Also practicing safe computing is very important. Don't put things like credit card information or passwords on the computer. Only visit safe sites. Keep your anti-virus software up to date. There are also options on the newer versions of IE and FireFox that will purge your cookies and history when you exit the software.
To have even more safety, unplug from the network or turn the computer off when not in use. That reduces the opportunities for exposure.
Using a different OS like Linux can reduce exposure as well since most security threats are windows based.
There's probably more, but greater security requires greater effort and expense.
-Sandy