First, I think of taking a drink, with both hands, from a big bowl. If you pantomime that motion, you'll see that your elbows go out and your wrists come in. If you add some extention to that motion, you've got a good kokyu movement.
Then, maintain that position with your arms while you rotate your hips.
I could show you the way we do it much better than I can explain it in words, but I hope this helps.