You can easily change Rulers units in Photoshop without going to the Preferences dialog. Just right-click on the Ruler and select your desired unit type.  →

Here are two very useful shortcuts to manipulate working space in Photoshop: Tab (Hide/Show Palettes) -  You can hide palettes to get more working space. F (Cycle Screen Modes) — You can switch between Screen Modes: normal screen, full screen with task bar without title bar, and full screen with black...