Floss your corset to make sure your stays, stay. Love this idea, my stays always shift down. I love the decorative aspect of it too!
Image from http://sidneyeileen.com/tutorials/corset-flossing/flossing-pattern1-med.jpg.
Japanese site! Gives step-by-step instructions on dressing in kimono/yukata, tying a variety of different obi musubi and some other useful basics (men's yukata/kimono, basic coordination of obi with yukata/kimono, dressing children for shichigosan).
DIY corset pattern, fitted exactly to you, with duct tape