An Extra Ounce of Prevention
Prior versions of Word had a "Fast Saves" feature that fortunately has been eliminated in Word 2007. (The feature resulted in larger files that had a higher chance of becoming corrupted.) One feature that has been retained from past versions, however, is Word's ability to automatically create a backup of a file whenever you save it. This can provide some excellent protection against dumb mistakes, like deleting half of a chapter. For some reason, Microsoft does not turn on the backup feature by default. But with backups turned on, you will always have a copy of the previous version as well as your most recently saved version. (Note that this is not the same as Word's AutoRecover function that only helps you in the event of a system crash or similar event.)
To turn on the backup feature, open the Word Options window, and choose Advanced from the left menu. Then scroll down to the section marked Save, and put a check in the check box for "Always create a backup copy". This change just may save your bacon some day. The only drawback to automatic backups is that they do take up storage space. While this is not a serious problem in today's era of enormous hard drives, you still may want to clean them out from time to time. (Fortunately, these backups use the .wbk file extension, which makes them easier to find.)
Choose a Different Default Font
Word 2007 comes with a bunch of new and attractive fonts, and uses them for some of its default styles. For example, the Normal style by default uses 11-point Calibri, which many people find to be a clean, sans-serif font. But perhaps you prefer a more classical look to your documents--say, a serif font like New Times Roman in 12 point, or perhaps even the typewriter-like monospace Courier New in 12 point. Luckily it's relatively easy to pick another font as the default for your documents.
Start by typing some text in a new document; then select the text. (Ctrl+A will select it all.) Use the Home tab on the Ribbon and change the text to the font settings that you prefer using the boxes in the Font section of the Ribbon. Then right-click the Normal button in the Styles section of the Ribbon, and choose "Update Normal to Match Selection". This will reset the Normal style in this document to your new settings.
Now, the next part may seem a bit strange at first, but hang in there. Change to the View tab on the Ribbon, and click on the top half of the Macros button at the far right of the Ribbon to open the Macros window. Next, choose the Organizer button on the Macros window to open the Organizer window. Then change to the Styles tab. You should see two lists of styles; one for your current document on the left, and one for the Normal.dotm on the right (as shown in the full-size screen shot). Select the Normal style in your current document, and then choose the Copy button.
You will see a message box asking if you want to overwrite the Normal style in the Normal template. Choose Yes, and the default font for your documents will be changed. The next time you start a new Blank document, your new font choice will show up as the Normal style font.
Lose the Wasted Space
Microsoft made another decision about the Normal style that you might want to change. By default, it leaves an extra 10 points of blank space after each new paragraph before the next line starts. If you prefer to have the spacing between paragraphs be single-spaced, just like the lines of text, here's how to make the change.
As before, create a new document and type a bit of text. On the Ribbon, switch to the Page Layout tab. In the section marked Paragraph, under the heading Spacing, change the After setting from 10 to 0. Then use Ctrl-A to select all the text (and the paragraph mark), and then switch back to the Home tab on the Ribbon. Right-click on the Normal style button, and choose "Update Normal to Match Selection". This will change the paragraph spacing for all paragraphs in this document.
Repeat the same steps as for changing the font in the Normal template. Use the View tab on the Ribbon, click on Macros, then Organizer, then the Styles tab. Copy the Normal style from your current document to the Normal template, and confirm your choice when the window appears. Now all your new documents will have single spacing between paragraphs.
It isn't hard to get Word set up to work the way you want, instead of Microsoft's guess at what's best for you. These six tweaks should make your work with Word more efficient. They also serve as an introduction for many of the places where you can easily customize the program to meet your needs. Explore some of the other settings, and you may find ones that can make a big difference.