Use the View Menu
Google has recently made a few changes to the menus in Google Apps. This is a good time to click on all the menus in your Google Doc and take account of what options are there, and which ones have moved.
When viewing Google Docs in Print layout mode (default) you can see a space between each page, as it would appear if you printed it. Save scrolling space by turning Print layout off. The margins and space between pages will disappear.
The default mode is Editing mode. However, Suggesting mode is really handy. Switching to Suggesting mode allows you to made edits as suggestions rather than outright change a collaborative document. A MUST when working with others.
I can't think that I've ever wanted to remove the ruler, but if it's getting in your way you can remove it!
Show Document outline
This is NEW! The Document outline option was moved from the Tools menu to the View menu. Take note! You want to have the Document outline activated. While creating your document notice the default font type is "Normal text." You can observe this right in the toolbar. When creating sections in your Google Doc use the Headings options instead of manually making the text bold. This will create the outline automatically in the sidebar. Notice the tiny triangle next to the heading selections. You can change the font for each heading and "Update to match" so that all of the text designated that heading will match that font style.
Show Equation Toolbar
Unlike the other options, this is selected off by default. Unless you're a math teacher (me) you probably don't have a lot of use to insert math equations into your document. If you do have a need to stick the quadratic equation in there you can toggle it on in the View menu. However, you probably would like EquatIO better than the built in equation editor. Note that it is FREE for teachers.
Show Spelling Suggestions
Spelling suggestions can get in the way when I'm trying to present with a Google Document or take a screenshot. Other than that, probably not much need to shut that off.
Need more screen space? You can hide the menus. You can also use the arrow under the blue Share button to collapse the menus. I point this out because once you turn on Compact controls, the View menu is no longer visible and you might go into a panic of how to get the menus back. Click on the arrow in the far right of the toolbar to bring the menus back.
If you want to hide both the menus and the toolbar you will want to view Full screen. Use the escape key to exit Full screen view.