In the beginning you can better ride your circles and turns a bit bigger.
By riding small turns, like changing hands by riding a S, you actually invite your horse to keep trotting small.
However, you want the hind leg to get underneath the mass and build a looser, bigger and ongoing movement.
Your horse will draw the line himself between stimulating and building tension.
Because whenever you cross the line, your horse will loose his good topline.
Imagine then giving your aid. Your horse will push himself up in the neck and he will get outside his comfortzone.
So make sure that your horse doesn’t go faster, but that he keeps following your hand and that you stimulate the hindquarters during the training.
Of course your horse needs to respond correctly to your forward aid. If he doesn’t, it also explains that he goes faster to create more impulsion.