I'm a big fan of shortcut keys. Years ago, when I first started supporting Macintosh computers professionally, I started working with a team of graphic artists. Now, I'm a relatively fast typist, and am decent with a mouse or trackpad, but these graphic designers were fast - really fast. I couldn't figure out how they could perform relatively complex tasks in Adobe Photoshop and Illustrator on-screen so quickly that it almost seemed like a blur of activity. Mesmerized by the activity on the screen, I initially failed to look down at not only the mouse, but the keyboard.
For the average computer user, the right-hand is primarily dedicated to using the mouse, switching back and forth when typing is required. Of course, the left-hand is used for typing as well, but what chores can you give this hand while the right-hand is busy with the mouse?
I rarely use exclamation marks in posts, but I wanted to emphasize their usefulness. First and foremost, most of the shortcut keys mentioned here will work - with slight modifications - on almost all computer systems: Windows, Mac and even Linux. You may have to use a different modifier key (Apple keyboards differ slightly from Windows-based IBM keyboards) but these modifier keys are always in the same general area on all keyboards: the lower-left (and lower-right).
My favorite shortcut is Undo. If you haven't learned this key, this should be the first one you master. It works in most programs, on most operating systems, and it's also the first key next to the modifiers: Z.
On a Windows-based system, just press and hold the Control (Ctrl) key, and while you are holding Ctrl, press the Z key. You've just undone the last operation you completed; whether it was typing a line of text, a circle you drew in a paint program, or a photographic tweak that just didn't work out in Photoshop. Undo (Command + Z on the Macintosh) is one of your best friends in the computer world. Not all programs support Undo, but the best ones do. If your program has a menu bar (File, Edit, etc.) you can usually click Edit and see Undo there. On the Macintosh, you will see the shortcut right next to the command itself.
There are so many other shortcut keys, although I'll run through a few of my favorites:
Cut: PC: Control-X - Mac: Command-X
Copy: PC: Control-C - Mac: Command-C
Paste: PC: Control-V - Mac: Command-V
You'll notice how the modifier changes (Control versus Command) between PC and Mac, but the key itself (X, C, V and Z) remains the same for the most basic shortcuts. While there are many shortcuts that only map to a particular operating system or application, the basics are worth learning on one, so that you are learning them on both. Undo, Redo (Ctrl-Y), Cut, Copy and Paste work in Microsoft Word, Excel and Powerpoint; Adobe Photoshop and Illustrator; and just about any application where undoing mistakes and copy-and-paste would be useful.
Although I didn't mention the Adobe Photoshop specific keys, I do want to say that many common functions in this photo editing program - such as (shortcut key capitalized) moVing, Erasing, Zooming, Stamping and Cropping can all be selected using your free left-hand, freeing up the time spent previously with mouse clicks and drags to pull down menus (cut/copy/paste/undo) or click on often-used tools (move/zoom/lasso/stamp).
Spending time mastering these basic shortcuts - and particularly the shortcut keys for those items you use frequently - will help you increase your efficiency when working with just about any computer application you employ regularly.