Most techie nerds will agree that Spybot is still a great option for free malware protection. Do a quick software download and then run the program to get rid of any sketchy files or applications that could be detrimental to your hard drive.
To free up some disk space (and make your computer run faster), go to the folder on your computer that houses your applications. Delete and uninstall any programs that you don't currently use, such as games you may have downloaded or other extraneous programs that are taking up space. Make sure, however, that you don't delete integral programs that support the main operations on your computer. If you aren't sure what the program is, do a quick Google search of the name. If it supports a program that you use frequently, make sure to leave it on your computer.
Downloaded documents and applications can easily pile up when you forget that they stay in the downloads folder long after you install a program or download a file from email. Throw away things you no longer need, have dealt with or have saved in your email. For the others, create appropriate files and organize documents and files in a detailed filing system that will be easy to pull up.
Desktops can get cluttered easily when you're working on the fly and not making or using a coherent and organized filing system on your computer. Taking the time to go through each file and program icon on your desktop will allow you to sort through and file random documents and get rid of things you don't need.
Cloud computing uses third-party programs to compute, access and store data virtually. Applications like Flickr, Picasa and Google Apps are popular ones, and uploading your photos, music and videos to these types of storage solutions can seriously ease the memory burden on your PC or Mac. Plus, it gives you access to your files from any computer, as long as you're connected to the Internet.
It seems obvious, but it's an easy step to forget. After you've cleaned out all of those old documents and programs, they're still lurking on your computer in the trash bin, and if you don't empty that folder, you're not going to see much improvement in the speed of your computer.