Re: Getting Accustomed to high falls?
As far as practical advice, mine is similar to NagaBaba's. Start on the ground and gradually add height while building muscle memory (and building core strength, which helps).
Also for some falls it can be helpful to have a big heavy partner who will stand there and let you practice self-propelled falls off their arm or belt.
Also some of the more advanced people in your dojo may be pretty good at throwing you in a predictable way and helping you get in the right position. IMO this is great for practice and to build confidence and relaxation.
I have known some people to find a crash mat helpful. Personally, I don't like it as much because it's so mushy that it's hard to control the position you fall in, but some people say it helps them build confidence and get a chance to try different positions without as much fear of pain or injury if it doesn't work.