Okay, you probably already know the ol’ Command-Shift-3 shortcut for taking a screen capture of your entire screen, and you may even know about Command-Shift-4, which gives you a crosshair cursor so you can choose which area of the screen you want to capture. But perhaps the coolest, most-secret hidden capture shortcut is Control-Command-Shift-3 (or 4), which, instead of creating a file on your desktop, copies the capture into your Clipboard memory, so you can paste it where you want. (I use this to paste screen captures right into Photoshop.)
Also don't forget Ctl + 2 finger scroll to zoom in!!