Save Early and Often! When you open a document of any sort, get it started, then save it. This confirms that the pathway to the place that you plan to save exists and that things are working properly. Then it is a simple matter to save it frequently (Apple-S or Ctrl-S). When asked 'How often should one save?" my answer is "How much are you ready to retype?"
Save your document before printing it. In the long list of things that can freeze a computer, a number of them are related to printing. It's a shame to have to restart a computer because of this before you have saved your work.