For viruses, worms and Trojan Horses, its a must to have a firewall on your home PC, especially if you're the kind to visit all sorts of websites and you have heavy downloads like ebooks. I'm using Sygate firewall, in addition an anti-virus is a must, any decent one like Norton, McAfee or AVG will do, please put up proper settings here in your anti-virus, there's a clock in the settings where you can opt for once daily automatic uploads of latest anti-virus software directly from the website, say Norton or whichever package you install.
Advice # 2-- Avoid visiting porn sites, if necessary you can visit porn sites from the cybercafe, don't do so from your personal PC.
Advice # 3--- Install the Google or Yahoo toolbar, a must. That blocks upto 95% of all pop-ups, which again are a source of viruses. I've installed both toolbars on my PC.
Advice #4-- Occasionally, you must delete all temporary internet files and folders from your system, these slow down the browsing after some time, can also habour viruses.
Advice # 5--- Install a anti-spyware package too.
Advice # 6--- Avoid saving your credit card numbers, all confidential bank account numbers, and all such confidential material on your PC, folks using spyware can gain access to your PC, and steal such information. For those with short memory recall, preferably save all such confidential material on hard copy, paper will do in such cases.