Re: Zagi Kokyudosa
Find a patient partner, and get into the arms-extended position from which you start the throw. Try to detect any tension anywhere in your arms, shoulders, or back, and relax it--without going limp or letting your partner push you around.
Then move forward into your partner a little further, till you feel resistance, and try the relaxing exercise again.
It is very hard to relax when in conflict with your partner, but if you can learn the trick of it your kokyu dosa will probably improve.
The other thing that really helped me with this one was being uke, and trying (without force) to stop the other person. Just sit there like a granite boulder, and try to understand the difference between times when your partner succeeds and times when he does not. There's a trick to resisting, at least in the form of kokyu dosa my school does, where you take partner's force and use it to anchor yourself to the mat, so the harder he pushes the less likely you are to move. If you can do this trick, you can also understand how partner is doing it, and find ways around it.