The one-hole bow has been around for a while, but just in case you've never made one, I've provided some directions below. What I like about this bow-making method is that the bow is always straight when it's finished. I typically end up with bows that are slanted to one side, but not with this technique.
First, punch a hole where you want the bow to be. I used a 1/4" hole-punch for my 1/4" grosgrain ribbon.
Next, place your ribbon on top of the cardstock. Be sure you cut a longer piece of ribbon than usual, because it will be wrapping completely around your cardstock before being tied into a bow.
Wrap the ribbon around to the back of the cardstock, then thread both ends through the hole from back to front. Pull one end out below the ribbon, and one end out above it.
Now tie a bow and you're done. I've attached this small element to a card, but this technique is also very effective when used directly on a full-size card, especially if you use a dramatic or fancy ribbon.