First of all - welcome to BC !
Assuming you have working antivirus already installed then perhaps the following, all available from BC as free downloads. If you don't have working A/V then selecting and installing one is your first priority ! I use the following but there are alternatives.
Ccleaner by Piriform. an excellent tool for removing temporary files which clutter up the system -
Note that one section of Ccleaner is a registry cleaner. You are strongly advised NOT to use these tools, see this image -
Then I would recommend the use of both Malwarebytes and Super AntiSpyWare which you can get respectively here -
Both of these come as free and paid for versions. The main difference is that with the free ones you have to run the scans yourself and they do not offer real time scanning. They are both anti-malware products but with a slightly different emphasis on the threats they search for. Have a look at them and make up your own mind which is better for you - paid or free - but I would recommend the use of both.
Over and above that, since prevention is both better and easier than cure, practice safe surfing. Don't open e-mail attachments unless you are certain you know who sent them. And even then be careful, it is extremely easy to spoof an e-mail sender's address. Don't be tempted to use software 'cracks', these are usually riddled with malware. Try to avoid 'dodgy' web-sites. And remember - if an offer sounds too good to be true, it probably isn't true !
One final note. There is a lot of good software out there on the web - a lot of the software I have is downloaded. If possible always download from the author's/publisher's site and when installing - ALWAYS use the custom install, NOT the quick or easy one. If there is something else attached custom install will usually allow you to de-select it before it installs.