I'm not a big fan of carrot stretches, to get a horse truly supple they need to be travelling forward.
As a rank beginner, I don't think you need to be thinking about shoulder in or even turn on the forehand as yet. The best thing you can do is start by learning to ride a solid 20m circle, getting your horse responsive to your leg and even in your hands. This is the first step towards developing a supple horse, it will create correct bend and flexion, and give an idea of an inside leg to outside rein feel.
Chiilaa is dead on with her suggestion, transitions, basic shapes, get activity in the hind end. Then the suppleness will come.
Just to note, Georgia&Felix, you may need to go back and look at your theory of shoulder in on a circle. If you are just pushing the haunches out, the horse is crooked and the exercise is useless. Shoulder in is just that, moving the shoulders in. The haunches MUST track straight on the circle, with the shoulders placed on a slightly smaller circle - it's a tough exercise when it's ridden properly!
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