There are always ways you can tweak your operating system to be more efficient. The problem with demonstrating these things in classes is that the more powerful they are, the more likely it is that one mistake can cause problems.
One of the tools in Windows that is among those is called MSConfig. Microsoft considered it so powerful that they chose not even to create a Start Menu shortcut for it.
MSConfig is a tool that allows you to do a bunch of things, but I think the best use is to tell your computer what programs should start up when the computer boots. You would be surprised at how much junk is set to load automatically, and it can be disabled with the click of a mouse.
The nice part is that if you accidentally shut down something important, you can also come back and switch it back on - you are not deleting anything, just disabling things.
I usually demonstrate it in classes, but someone has done one better and listed step by step instructions on how to do it in most versions of Windows.
Once you visit that site, scroll beneath the ads and click on the version of Windows that you are running.