This is the method I used to make my bows for Eternal Sailor Mercury, and similar to what I use for most of my bows, especially the very stylized Sailor Moon manga bows or any bows where rectangles just don't give the right shape.[link]
This is the pattern I refer to in the tutorial. Feel free to print and use as is, or modify it for your purposes!
The pattern is for a small manga style Sailor Moon chest bow.
Recommended fabrics: matte satin or taffeta (needs less interfacing!)-Please follow my cosplay on Facebook-