best for me was to drill a hole in the front on my longboard skater and clip a rig to it.
5 to 10kn with a small sail in a carpark and was nailing gybes and duck gybes in no time.
use old gear
timing that flip and keeping it in the power zone was the trick.

In my case I needed to establish some muscle memory first as I was getting stacked and confused on the water. So I set up the board with half mast and boom (no sail) in the living room in front of TV and practiced 3 times a night for about 20 minutes. It's really great for getting the foot change, hand change, sliding the hand to the mast before the change, bending the knees etc into sub consciousness. After couple of weeks I didn't have to think about it on the water as much. It came up quite naturally.