At a risk of posting a redundant thread I am asking all of you generous folks to post some of your hints, tips, shortcuts and other sort of things that you feel will benefit other users. What I'm really interested in is the type of (typically) unknown quickies that other users may not know about. Please provide a short summary of the tip/shortcut/etc and a possible example.

As an example:
To quickly fill in the remaining text for a filename, command, etc from a command prompt is to type in a few characters of the command name and then press the 'tab' key. This will allow the system to fill in the rest of the values and prevent you from having to fill in the rest.
Try typing in the command: ls /boot/bz and then -tab- which should fill in the command line with: ls /boot/bzImage

Thanks in advance