There is a nice vid over on Master of YoYo which I think shows the wrist motions on inside loops well:
http://www.masterofyoyo.com/2a-looping/inside-loops
Note when he says the the yoyo flips over on every loop, causing the string to loosen for righties, and contributing to the tendency for it to get “twisty”. There’s an outside loop vid also, but the link’s not working atm.