How to ride a proper Circle
There are two things to think about
How the CIRCLE is being ridden geometrically.
How the HORSE is being ridden on a curved line
Remember, in a circle you should NEVER NOT BE TURNING.
Another mistake is often you will be doing a great job until you reach the side of the arena then end up moving along the rail of the long side for a few strides, all flat. Then you realise you need to turn to get to your next ‘circle point’ and veer sharply off the rail to make it to center line in time. Now you have made a twenty meter shape with some flat sides instead of a circle.
Think of it like this, if you have ever seen tennis balls inside their plastic packaging cylinder, you will notice that they only just touch the edges of the ‘long side’ and ‘short side’ of their container with no flat bits . A circle in a dressage ring is the same, with us always having to ride into, onto and out of every contact point, no matter the size of the circle. If you are on the rail for more than one or two strides then you have been at that point of the circle for too long and it is no longer circle.