There are loads of Mac keyboard shortcuts that can make your computing life much easier. Assuming you already know the basics such as cutting and pasting text and quitting an application, here's a more intermediate resource that should help you speed up your day-to-day activities a bit by saving you a few trips to the menu bar. (If you would like to check out something more basic to make sure you’re totally up to speed, we recommend checking out MacWorld’s excellent beginner’s input device guide.)
Get Info: Command + I or Command + Option + I
This brings up the Get Info window in Finder, which shows you things like the file’s name, type, and size. If you also press the Option key, you can select several files or folders and it will bring up a single collective Get Info window for all the files.
Show/Hide the Dock: Command + Option + D
Have you ever had one of those moments where you needed just a tiny bit more screen real estate to look at something? This allows you to quickly toggle hiding and revealing the Dock.
Create a New Folder: Shift + Command + N
Using this command will create a new folder in Finder, within whichever directory you’re in.
Empty the Trash: Shift + Command + Delete
It’s a good idea to periodically empty the trash; if only it were this quick in real life.
Close a Window: Command + W
This is handy if you want to close a single window or tab in an app without hiding or closing all the windows for that app. Make sure the window or tab you’re looking at is what you want closed.
Create a New File/Window: Command + N
Say you want to create a blank document or launch a new browser window--this command will create one for you.
Open a File: Command + O
If you need to open a file, this command will launch the Open File dialog box.
Browse Forwards or Backwards: Command + [ or ]
If you find yourself wanting to go backwards or forwards in your navigation of Finder or an Internet browser, type this and it’s as if you'd clicked the arrow buttons in the toolbar.
Start Spotlight: Command + Space
If you’re not yet using Spotlight, you really should be. This command brings up the Spotlight window for you to begin typing whatever item you would like to search for.
Undo or Redo Actions: Command + Z or Command + Y
In most apps, if you do something you don’t mean to do, you can undo actions with Cmd + Z. If you get a little carried away and want to redo something you’ve undone, hit Cmd + Y.
Switch Between Apps: Command + Tab
Do you ever find yourself frequently cutting and pasting between apps? It can seriously speed things up if you are able to switch between apps with just a few keystrokes. This command will allow you to do that.
Switch to Hide or Quit Apps: Command + Tab + H or Q
If you’re done switching back and forth between apps, hit H to Hide the app or Q to Quit it.
Quick Look: Space or Command +Y
Want to see what’s in a file without starting up the app associated with it? You can type Space or Command + Y to open a window that allows you to view or listen to a file (but not edit it, of course).
Start a Slideshow: Option + Command + Y
Adding Option to the previous shortcut will allow you to quickly view a whole bunch of files at once, like a slideshow.
Jump Words: Option + Right/Left Arrow
If you want to move through text a little more quickly, you can move one word at a time in either direction by hitting Option + the arrow for the direction you want to go. (For bonus points, if you also hit Shift, you will select everything between the cursor and the place you jump.)
Jump to the Start or End of Lines: Command + Left/Right Arrow
If you want to move through text a little quicker still, you can move to the beginning or end of a line by hitting Command + the arrow for the direction you want to go. (Once again, if you also hit Shift, you will select everything between the cursor and the place you jump.)
Jump to the Start or End of a Section: Command + Up/Down Arrow
If you want to go to the beginning or end of a paragraph, hit Command and the up or down direction as appropriate. (Yet again, if you also hit Shift, you will select everything between the cursor and the place you jump.)
Forward-Delete: Function (Fn) + Delete
Every now and then, it would be just a bit easier to edit your text if you can delete forward instead of the default backwards direction. This command allows you to quickly delete text at the right of the cursor.
Select Rectangular Block of Text: Option + Drag
This is a trick that may not often be useful, but when it is needed, this command can totally blow your mind. If you just want to select a rectangle of text rather than contiguous lines, hit Option and drag to highlight your rectangle of text.
Paste with Target Format: Shift + Option + Command + V
This command will require you to do a convoluted hand maneuver that may well take you just as long to form as finding the menu option until you get the hang of it. But once you do, this can really speed up your word-processing.
If you would like a more comprehensive guide to OS X shortcuts, visit Apple’s reference guide. And if you would like an app that can give you a quick cheat sheet of keyboard shortcuts for OS X as well as other apps, try the free CheatSheet.