Sometimes you can make your circles better by not working on circles! Work on squares, 90 degree turns, and diagonal lines for a while, and maybe some nose to the wall leg yield. Then come back to your circles, after you have worked on better use of and response to your outside turning aids.
Acceptance of the outside rein is key to resistance free downward transitions.
You should feel like you have to ask your horse to stop, rather than simply "letting" him stop. If he stops when you let him, he is behind your leg.
To successfully maintain the elusive forward feeling hands, imagine that you are pushing a shopping cart as you ride forward into the bit.
Horses speak through their actions. Try to listen to what they are telling you.