One thing you often forget is all the shortcuts windows offers. Ctrl + C and Alt + Tab and other short cuts are used all the time but there are more, somewhat hidden, shortcuts. Especially using the windows button.
Here’s a list of some of the most useful ones :
Win + D
Show the desktop
Win + M
Minimize all windows
Win + Shift + M
Restore all minimized windows
Win + E
Open up a windows explorer
Win + F
Search for a file or folder
Ctrl + Win + F
Search for other computers
Win + L
Lock the desktop
Win + R
Open the run dialog
Win + U
Open the Utility-manager (in Vista this will open the horrid Ease-Of-Access center, so be warned 
)
Well, these are non-essential but useful things to know about how to use your operative system. There are more shortcuts, but these are the ones I generally use.