Originally Posted by NBEventer
If he is tricky go back to just a simple change with one trot stride. As he gets it smoothly with the one trot stride you only bring it to a huge half halt and switch your outside leg and ask for the new lead
I disagree with teaching the change through the trot. If done too many times before asking for clean changes, you can easily teach the horse to "cheat" by dropping to the trot for that momentary beat and produce partial, incomplete or messy changes. I true simple change is done through the walk. Again, it's not to be overdone. Once you know your horse understands what you're asking for, ask for it the correct way, so he doesn't get used to crutches.
I personally have been using a shallow figure 8 pattern and asking for the changes in the corners after each diagonal.