The 2.0 Life has a great article on Time Saving Tips for Your Computer.
I knew some of them, but found a few more that are great. Many of them are keyboard shortcuts that allow you to do things that would normally take more time to do. An example: Show Desktop - Press Windows-M (the windows key between ctrl and alt and "m") on a PC. Instead of closing or minimizing all of your open windows, you just press F11 and it minimizes all of your windows so you can see the desktop to get at files and programs.
These tips can make you more efficient while using your computer.
