Make your dress. I used an existing BCBG dress with an elasticized back (for during / post pregnancy purposes) to create a paper pattern for my new dress. (Note that this works best for simple dresses made from 2 basic pieces - front and back. Any dress featuring ~4 + pieces [front torso and skirt, back torso and skirt] will be more complicated especially if they feature darting.)

Sew and edge the following (you can adjust these sizes if you'd like your bows larger or smaller):

2 rectangles of 6.5x13"
1 rectangle of 5.5x11"

Create your bows. Here I'm using ribbon to demo because I played around quite a bit when I made the dress bows before settling on a method. Take the rectangles you just sewed in Step 2 and pleat them down the middle. Stitch all the way through the center of your pleats several times to secure and knot. You should not be able to see your stitches from the front of the bow.

Pleat down the middle.

Stitch through all the pleats (for easy demo purposes, I'm just pinning them)

Arrange your bows. I criss-crossed the 2 longer rectangle bows and then crossed it again with the 1 shorter rectangle bow. You can do this on an angle covering more of the right shoulder like I did (also fabric is going to create much prettier drape than the stiff ribbons used in the demo photos).

Criss-crossed with the 2nd long rectangle bow

Crossed one last time with the short rectangle bow

Hand tack the bow ends onto your dress. See the stitches right above the "Gal" portion of the center "SewPetiteGal"?

And you're done!