This is such a quick little tip that you might not think that it matters, but it saves a few seconds every time you close a document. If you close a number of documents a day , it really starts to add up fast. When you close a document, Photoshop presents you with a dialog asking, "Save changes to the Adobe Photoshop document before closing?" You have three choices: (1) Don't Save, (2) Cancel, and (3) Save.
Here's the shortcut: Press the letter D for Don't Save, press S for Save, and C for Cancel.
Want to change the unit of measurement for your image? Don't go digging through
Photoshop's menus for the Preferences dialog, just Control-click (PC: Right-click) on
Photoshop's rulers and a contextual menu will appear with a list of measurement units.
(Note: If your rulers are not showing, press Command-R [PC: Control-R]). Choose the
one you want, and your rulers will instantly reflect the change.