Change Guide Direction

As in many applications, you can add non-printing guides to a document by clicking on one of the rulers and dragging onto the document. As you click on a ruler and drag a guide onto the document, the guide will be based on the ruler you've used (top ruler creates horizontal guides, side ruler creates vertical guides). To override this, press the Option key (PC: Alt key) as you drag from the ruler and you'll get the opposite guide. (Press and release Option/Alt to switch back and forth.)