Re: Ukemi and Koshinage
Every place does it differently, as stated above, so you'll have to sort through various answers and pick the ones that best fit your current training. Learning break falls / ukemi in general over the internet is not recommended. Having said that, I do have some suggestions from my perspective:
1 Buy a copy of Ellis Amdur's Ukemi from the ground up, grab a senior, watch it together, and try to implement in seperate practice. Learning from a video is never really recommended, but having been in some of his ukemi classes, I have to recommend it any way. Having a senior there can really help to work through some of the issues you are bound to run into.
2 Work on making your body curl. When I'm thrown in koshinage, I REALLY tuck /curl my head and upper body so that I'm looking back at nage almost even before my legs go over. This is the exact opposite of the stiff as a board crowd. I believe that ukemi should be opening me for sutemi when it comes to koshi throws.
a) If a judoka or someone used to competitive grappling is throwing you, they are coming down with you. To reverse them you once they've gotten the lift you need to curl and roll them through.
b) I like to not depend on nage's kindness. Even when giving up control I like to re-establish control at the same time.
c) I like to train to not need to grab for koshi ukemi...in my opinion, it develops a dependancy you can't count on, or that can give nage an additional handle for a lock once you hit the ground. I understand that it is a stage most have to go through (me too), but I don't always agree with it.
The more you curl the more possibilities open up, for sutemi, for rolling, for break fall to standing up immediately and gaining distance by using the straight leg.