Switch between your active Excel windows using the Ctrl+F6 shortcut. In Excel 2010, it will toggle through all of them. In 2013, it will only do the last two.
Minimize a window with Ctrl+F9. When working with multiple workbooks or work sheet windows, it’s handy to be able to minimize the one in front of you, so you can see the one hiding behind.
Maximize your window by hitting Ctrl+F10. If you’ve assembled a particular arrangement of windows to facilitate your Excel tasks, it is really nice to go full screen on any one of them and then back to your preferred arrangement.