Just do more and more with your body and less messing with his head/mouth with your hands. Make sure to look where you want to go and have your body follow. Most of all be consistent with your cues! Every time you want to turn left it should feel the same to your horse and every time you want to stop it should feel the same to your horse.
The best way to achieve this is by riding with a loose rein. I mean a draping rein like what you would see at a Western Pleasure show. If you need to you can make contact, but there is no reason to always be making contact. The VERY last thing you should do is take hold of your horse's head/mouth. This is how you should cue for a turn: Look, Leg, rein. Each occurring if and ONLY if the one before it didn't get a response. Upward transitions are fairly simple, bring your energy up. Downward ones you just stop riding (kinda get limp, but don't fall off) and your horse will mimic you, but be sure to start riding again when you are going the speed you want. And to stop, curl your back, say whoa and exhale deeply (this thrusts your pelvis, or you could cough, that can work better) put all your weight in your but bones and sink into the stop while looking at your belly button. Until your horse understands this you will probably need to use your reins, but over time you will have to use them less and less.
Remember, only do as much that is neccessary and build your cues up gradually, start at 1 and then go up 2,3,4,5,6,7,8,9,10. Don't start at 5 and go straight to 10. This will get you nowhere, but if you gradually build than you will find that you don't have to go as far up as you keep progressing.
Best of luck to all of you. Feel free to PM if you have questions
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