I've been having trouble consistently nailing my ochos. As soon as I stopped having such a wobbly axis, I seemed to have trouble pivoting enough - and with enough disassociating to make the step look and feel smooth, graceful .. and precise.
I got a bit of advice from my instructor Monica, who I believe she said she got from Silvina Valz, regarding turning during ochos. She said pivot until you can see your butt (over your shoulder). How literally you take that is, of course, up to you. To my surprise, I found it incredibly helpful in remembering to disassociate my hips and first of all, not use my partner for leverage, and second, it gave me something more tangible to monitor my consistency.
Do you have other ways you monitor how a step or movement needs to "feel" or look to know you've completed it correctly?
(PS - that's me looking for my ocho booty and modeling my new Flabella tango shoes. :) )