[EDIT: The following post is completely wrong. Please ignore it.]
The setting that causes this is in the Page Setup dialog, which you can open by going to File > Print and clicking the Page Setup link at the bottom of the settings. It's also available by double-clicking the horizontal ruler, or by clicking the launcher arrow in the bottom right of the Page Setup group on the Layout ribbon.
If you choose Mirror margins in the Multiple pages dropdown, Word will force all odd-numbered pages to be on the right side of each two-page layout, and all even-numbered pages on the left side (this is the standard publishing convention). Since there is no even page before page 1, Word prints a blank, although there's nothing in Print Layout view to indicate that. (If you set the zoom of the preview on the File > Print page small enough to display two pages at a time, you'll see page 1 alone on the right; then pages 2 and 3 together, etc.)
Instead of Mirror margins, choose the Normal setting in the dropdown. That will print page 1 on the front of the first sheet, page 2 on the back of the sheet, then page 3 on the second sheet and so on.