Turn on the forehand and leg yield can be used to teach the horse that the rider's leg can mean something other than, "Go forward."
The horse must understand this concept in these very basic movements before you will find much success with any of the more complicated lateral movements.
"Suppleness means that the muscles contract and de-contract, and this has to go through the entire horse, it cannot be blocked in the middle of the back, and it also has to go through the rider." ~ Susanne Miesner
"The less we do on cross country, the easier we are on our horses. Learn how to be more still. Don't touch their mouth unless you need to. Plan your turns." ~ William fox Pitt
Impress your Dressage judges by showing a clear difference between riding a corner and part of a circle.
"The rider's seat is a 'transformer' whose role is to modify the energy emitting from the horse's haunches." ~ Charles de Kunffy