I've been asked this question almost over 1000 times and so I thought I would write a small article on the same. If you have the same question in your mind, follow..

In the first place, you should know that the Media files such as the Movies/Videos take up huge space. And in this world, its very cheap to find an External Hard-drive just to store your Entertainment stuff exclusively. Apart from the media, there are some programs like Adobe Photoshop, Encyclopedias and various other softwares that you use may occupy a whole lot of space. I'm not telling you to get rid of them but just make sure you install them on the right partition of your Hard-Disk and keep away from those programs which you really never use.

Over time, Windows accumulates a lot of junkware in your hard-disk such as the temp folder with all temporary downloaded files, installation files, error logs and lot. Most of the programs that you install, are supplied in a Setup Packages which is compressed. Before install, they usually unpack themselves into the Temp folder and fail to remove themselves automatically after installation and always get unnoticed by you. Now the best thing is, Windows itself has a very good Disk CleanUp Wizard. There are ofcourse some third-party softwares that boast themselves to clean-up your computer and beyond being priced, they may also delete some important files which might leave you in disaster. So I better stick with Windows' own Disk Clean Up wizard and would recommend you the same too.

You can access Disk CleanUp wizard from Start > All Programs > Accessories > System Tools > Disk Clean Up Wizard

Once you're there, you will be presented with what you want to delete to make your system clear. They can easily do the following to remove junkware from your system.

• Delete downloaded program files - these files are automatically downloaded by Internet Explorer and can be deleted safely
• Delete Temporary Internet Files - Internet Explorer saves some temporary files when you browse. These files can be safely deleted
• Deletes Off line Web Pages - Pages that are stored for access while you are not connected to the Internet.
• Empty Recycle-bin - When you "delete" a file, it's not really deleted. Emptying the recycle bin frees up a large portion of storage space in your hard-drive
• Deletes temporary files - The files that I have explained above. Safe to delete them
• Delete Error Logs - When windows encounters an error, it saves a bit of information which you may never need. Delete them safely

So these are above things that the built-in Windows Disk Clean Up Wizard will let you do. While the operation may take long, you can go for a coffee after you have chosen the options and pressed the Clean Button.

Performing the above regularly will keep you system definitely clean. It is also recommended to perform a Disk De-fragmentation after the clean up so you will notice a huge performance improvement over-all.