I recently switched from a Windows laptop to a MacBook Air, so I'm keeping track of shortcuts as I learn them.
In the Terminal, move between tabs using CMD + SHIFT + ] for right and CMD + SHIFT + [ for left.
Hover over a word and press control + command + d to get a dictionary lookup; or use three fingers on the trackpad.
In Finder, go up a directory by pressing CMD + UP
In order to find out the location of an application in the Dock, hold down CMD and click (don't hold) on the icon.
Maximise a window (like in Windows) by clicking the green + with shift.
Capture some of your screen by pressing CMD + shift + 4
brew install wget