If you're using up to Word 2003, you can press Ctrl-D to load the Fonts dialogue box, set all the stuff you want and then click the button in the bottom left to update the normal stylesheet based on your specifications.In Microsoft Word, how so I set the default style to be 12 pt. Times New Roman rather then 11 pt. Calibri?
If you're using the new style of Word with the ribbons and different layout etc., then if you click the Font Style ribbon drop-down box, there should be an option to set some custom setting and from there update your Normal stylesheet.
As an aside, use Arial rather than Times New Roman. At small font sizes, all the serifs tend to crowd the letters and make the page look untidy.