The OS X Finder has a number of shortcuts and features for previewing items, navigating through folders, and selecting items to open. These can be quite convenient when browsing through your documents. If that's the case, you might be interested in knowing several of these are available when browsing through documents in the system's Open and Save dialog boxes as well.
Even though you may be in a program like Pages, TextEdit, or Microsoft Word, the Open and Save dialog boxes in these programs essentially open up a window to the OS X Finder so you can browse for documents and locations to save new files. As such you can make use of various Finder features, including the same sidebar to the left that contains your custom favorite locations. But there are a few hot key shorcuts you can also use.
If you open the Go menu in the Finder, you will see a number of locations you can immediately jump to, along with a corresponding hot key. For instance, to go to the Desktop you can press Shift-Command-D, or to the Documents folder you can press Shift-Command-O. These shortcuts can also be used in Open and Save windows, to quickly navigate to the respective location.
In addition to the direct shortcuts, you can use the Finder's Go To Folder shortcut (Shift-Command-G) to navigate to hidden locations on the system. This can be convenient if you have a program like TextEdit open and wish to directly open a hidden system configuration file or two for editing.
Besides the location hot keys, you can use the Finder's navigation hot keys which are primarily the arrows in combination with the Command key to move up one directory (up arrow), open the selected item (down arrow), or expand or collapse items such as directories in list view. Furthermore, the standard Command-O will also open directories and files. In Save dialog boxes, Command-S will save files in addition to pressing Return or Enter.
If you inadvertently displayed the Open or Save dialog box and do not wish to open or save a document, you can close it by clicking the Cancel button or by pressing Command-Period, which is the universal cancel hot key in OS X.
Beyond navigation, there are two additional separate hot key options for the respective Save and Open dialog boxes. When in Save mode, you can create new folders by clicking the "New Folder" button but can also do this by pressing the standard Shift-Command-N hot key as is done in the Finder.
Lastly, in Open dialog boxes you may wish to preview your current selected document before opening it, which you can do to an extent by entering Column view mode. However, if you wish to have a more detailed look, you can invoke QuickLook in the Open window by pressing the Space bar with your target document highlighted.