http://www.businessinsider.com/mac-tips-and-tricks-2013-7#take-a-trimmed-screenshot-tired-of-taking-screenshots-that-capture-much-more-of-your-screen-than-youd-like-hold-down-command–shift–4-which-will-change-your-cursor-into-a-cross-hair-after-youve-outlined-what-you-want-to-be-in-the-screenshot-press-the-spacebar-to-capture-1

Command + Shift + 4 = Screenshot of area

Command + Q while cycling in apps list quits the app, Command + H = minimize

Command + Option + D = Will hide your dock. To restore it – repeat the key combination