A few steps to make your web browsing safer:

1.Genuine copy of Windows:

If you have a genuine copy of Windows, you'll be able to get all updates from Microsoft. These are general stability and security updates. No program, no operating system is completely safe. Criminals are trying to find exploits and use them against your computer. Having your system fully patched is the first and the most important step to stay clean.

If you cannot afford to buy a legitimate copy of Windows, use one of the free operating systems – for example Linux based systems. They can be harder to learn and use but if all you are doing is browsing the web, writing documents, editing photographs, listening to music or playing some card games, then this can be a good alternative. And most Linux versions are completely free!
Ready to try Linux? Here's how to get started: Linux: A Getting-Started Guide
You can learn more about Linux here: Linux New User Guides

Make sure you have automatic updates enabled or check manual updates at least once a month. windowsupdate.microsoft.com

2.Antivirus, firewall, antispyware:

Do you always try to keep your personal information safe? So why aren't you protected from internet threats?
Have you heard about hackers, spammers, viruses, trojans or maybe even about rootkits? Do you think that you are not at risk?
The truth is, everyone is a target. Criminals are continually trying to steal your personal data, sell you a worthless product or use your computer as a Zombie – they are just making money. Great amounts of money, unfortunately.
You need protection. Not only from viruses, but also from trojans, keyloggers, rootkits, spyware, etc... Malware can hide everywhere – in your mail, on your favorite site, in a link sent to you via an instant messenger program, on your flash drive...

To be protected – use an antivirus, a firewall and an antispyware program. Make sure you use only one program of each type in resident mode, so there are no conflicts.
You don't have to necessarily pay for them. There are quite a few versions available for free. See the list of proposed programs here: list

Am I well protected if I have these three types of programs on my computer? Actually, no. You should also have them fully updated. Antivirus programs must have the latest virus definitions – make sure it updates them regularly (some vendors update their definitions a few times a day). Check for updates of definitions in your antispyware program and make sure you have the latest version of it.

3.Keep your programs updated:

Do you know that having an old version of Java can lead to security problems? Do you know that using an old version of your web browser can be a security risk?
Many programs that you use on a regular basis are updated from time to time to not only improve them, but also to fix security issues. These can be programs like: Java Runtime Environment, Adobe Flash Player, Adobe Acrobat Reader, Microsoft/Open Office, Internet Explorer/Firefox/Opera…

So don’t take the risk! Always have the latest version of the program.
Secunia Software Inspector is a nice tool which will check your computer for insecure versions of programs installed, as well as for Microsoft patches. Use an online scanner or download their free tool: here (see the tutorial on using it on BleepingComputer).

Other programs of this type: FileHippo.com Update Checker (requires Microsoft .NET Framework 2.0) or Appupdater.
You can also check for outdated plugins in your browser at Plugin Check or Qualys BrowserCheck.

4.Think while browsing, downloading, receiving e-mails:

If you want to download a crack or a keygen, think twice.
If you want to visit a porn site, think twice.
If you don’t want to read what you install, don't complain about getting infected...

Most malware is hidden on porn sites, on sites which provide cracks and/or keygens. However, your computer can also get infected on innocent looking or legitimate (but compromised) web sites. Just try to think while browsing – read what you click, install, what site you’re trying to reach… Be extremely careful when it comes to banking services – be suspicious when you are asked for a password or a security code. Don’t click on every advertisement banner, especially on those claiming to clean or scan your computer ‘for free’. Download video codecs only from reliable sources. Don’t ignore Google's or your browser's messages informing you that the site you’re trying to visit can bring malware to your computer.

Do not open e-mails you didn't expect to get. It will probably be just a spam. If you read your e-mail in a web browser, make sure the site provides an antivirus scanning of attachments and automatically redirects messages considered as spam to a special folder. If you use a program like Outlook Express or The Bat to read your e-mails, you can use a program named MailWasher - it lets you manage all the messages before downloading them, so you can filter out any unwanted e-mails. Make sure all attachments downloaded or opened are scanned with antivirus software.
For more information see my short article here: Spam (e-mail)

5.To increase your chances of staying clean:

The first thing – a web browser. I recommend you use either the newest version of Internet Explorer or an alternative, secure browser, like Firefox, Opera or Google Chrome - test and use the one you like best.

The second thing – passive protection. It means it will protect you without a need to run on startup. This includes: immunize feature in Spybot Search & Destroy, Spyware Blaster, a well designed Hosts file – for example The MVPS HOSTS file.

With Windows Vista, Microsoft introduced a User Account Control (UAC) feature. It's an extra layer of protection. Some find it annoying, but I believe that if a few extra clicks a week can make your computer more secure, it's worth having that feature on. That's why I suggest you keep UAC enabled - instructions for Vista and Windows 7.

If you use Firefox and want an additional layer of protection, you can install special Add-ons – like NoScript, which will block JavaScript, Java, Flash and other plugins from being executed unless you allow it. It prevents exploitation of security vulnerabilities, see the article here: Blocking JavaScript in the Browser. There is also Adblock Plus Add-on - it will block most of the advertisements on the web.

If you have children or your computer has many users, and you are afraid of them infecting your computer, you can use a sort of a parental control software. K9 Web Protection is a content filtering program for a home computer. It is easy to use and gives you a higher level of protection.

It is very, very important to have hard to guess passwords for your mail, bank account and for any other sites (Create strong passwords). It is recommended to use a different password for each site. Hard to remember all of them, isn't it? KeePass is a completely free program which keeps all your passwords safe – you need to remember only one password. It encrypts password databases, has a portable version and a random password generator as well. Familiarize yourself with its features.

Ever wondered if you should click on a link provided by your friend, a search engine or an advertisement? You can quickly check if it is not an exploit page - use a LinkScanner Online. You may also check if the site is secure (check its rating) on McAfee SiteAdvisor's page or on Web Of Trust's page. You can also alternatively install their Add-ons for Firefox or Internet Explorer for the real time ratings.