One of the first programs you should install is a good antivirus program. Fortunately (or unfortunately, depending on how you look at it), there are several good ones available. There are a few good free ones as well as some excellent paid options. There are several well known names like McAfee, Norton, Kaspersky, Trend Micro, Panda, Avast, ESETNOD32, etc, etc. With so many options it can be confusing as to which one will suit your needs better. In my opinion there are a few AV programs that used to be the standard and actually pretty good. Unfortunately they have become almost as menacing and annoying as the viruses and malware they are supposed to protect our systems from. The best thing is to do your own research and find out which ones have a bad rap amongst the techies (the geeks and nerds to whom you take your computers to get fixed).
Here are a few forums that give opinions about various programs: Norton, Kaspersky, Trend Micro, McAfee. As you can see, everybody's opinion varies. Some of the free programs that I work with on a regular basis and haven't had any problems with are Avast, AVG, Comodo, and Microsoft Security Essentials. Here is just one security challenge project that tested some of the more popular AV programs. Take a look and see how they measured up. There are also some paid versions to these that offer some extra features and protection. Avast has just integrated a remote assistance feature in their AV program that makes it quite convenient if case you need help from a techie friend. As long as you have internet access you can allow someone temporary remote access to your PC to try and help you. One AV program in particular called ESETNOD32 is quite light weight (uses very little system resources) and even lets you know if your Windows Updates are out of date. In my opinion, ESETNOD32 is one of the better paid AV programs out there. One other paid AV program worth mentioning is PANDA AV. They have been around for quite some time and seem to be doing a good job at expanding and keeping their databases up to date.
As for myself, I tend to overlap protection in order to keep my system as secure as possible (even though nothing is 100%). By this I don't mean to install 2 or 3 AV programs. Doing so can make your system unstable and cause it to crash. I use other programs in addition to my AV program to run on demand virus/malware scans, cloud based virus/malware scans, and USB based viruses protection. One popular program is HITMAN PRO. This program needs an internet connection to work and uses a cloud based database to analyze your files for any know malware/spyware/viruses. There is even a portable version floating around in cyberspace that can be placed on a usb drive used on any PC without installing any files. Another program called ClamWin Portable is the portable version of the popular open source AV program ClamWin that has been around for years. I also use Malawarebytes to run on demand scans for any malware or spyware that may be lurking in anything I download or have on my PC. Last but not least, I use a program called Panda USB Vaccine. Since most of us use USB flash drives now a days, they have become one of the most popular way to spread viruses and malware from pc to pc. Most USB flash drives have a certain file that allows Windows to immediately recognize it and want to run some sort of program from it. This is an easy way for a rogue program to infect a new system. This program eliminates that autorun file and keeps your USB drives from running anything unless you specifically open it up and run it. It also gives you the option to "vaccinate" your computer so that any other USB drives you insert in your PC will be automatically "vaccinated" as well.
A helpful tool that I use on a everyday basis and install on nearly every PC that I work on is a program called CCleaner. This program is quite convenient and integrates some of the clean up tools that Windows has into one simple to use interface. It can clean up your recycle bin, temp files, cookies, etc. It has a utility to uninstall programs and also has one to stop programs from starting up upon Windows boot up process (helping your system start up faster). It has a registry cleaner utility as well, although I wouldn't recommend using this unless you feel comfortable making some changes that could potentially hinder your system if you weren't sure about the changes you were making. Here's a quick description of the program and you can download one of several available versions here.
You should also defragment your hard drive on regular basis, depending on what exactly you do and how often you use your computer. Here are some of the benefits of defragmentation. You can either use the built in Windows defragmentation utility or there are some alternatives that work just as well, if not better.
Of course there is always the golden rule when dealing with computers. "There is no substitute for redundancy." Always make sure to back up your important data. Make a complete system image if possible, just in case you ever have a total meltdown of your system and need to recover it to exactly the way it is now. If you have data that is extremely vital then I suggest not only backing it up to an external hard drive but you may want to make a copy on some sort of physical media such as digital tape, CD-RWs, or DVD-RWs and keeping them in a scratch proof container and in a safe, cool, and dark location.
Hope these tips can help someone out there. I'm just trying to make this world better by sharing information. As always, any tips, comments, rants, or kudos are welcome.
CARPE DIEM!