On of the best things I have done to improve my computer skills and efficiency while using my Apple computers over the years is to learn shortcuts. Certain keystrokes are common knowledge, but others are less widespread.
Here are the basics:
COM+C/COM+V & COM+N - Copy/Paste & New 'whatever'
COM+Z - Undo
>>Most used by Your's Truly
COM+TAB - Last application opened; hold COM & tap TAB to cycle through (or use mouse to select)
>>Super fast app switching (Not that you would be Facebooking in Safari & working in Firefox or anything...)
COM+` - (it's next to the 1 key) toggle through a single applications multiple windows
>>If you are compiling data in Word/Excel from multiple files this is great (or listening to Pandora while browsing in a second window)
COM+1.... - Switch to Spaces (1-10); also try COM+arrows...
>>Organizes work spaces
SHIFT+COM+F - Full Screen
>>great for presenting or just removing distractions
COM+SPACE - Spotlight search
>>I never use the Finder anymore
Okay, well try those out and if you have a favorite share it here!