Lots of circles and squares, try pulling him in a medium sized circle till you really feel him give to your cues, then stop and reward him with lots of pats, just repeat this for a while till you really feel like he is in tune with your cues, hope this helps! :)
Spend a lot of time working on the ground with him, go for walks (on feet too), play with him, try to learn him some tricks on the ground like follow me etc..
This will really help you
Try to change what you are doing and never repeat things. For example instead of just going around the ring, do circles, change directions, do different exercises like the broken line or (I’m not sure what the correct term for this one is but...) the teardrop as we call it. Having poles out is also a great idea because it can make the ride exciting and will make them pay attention to where their legs are going. Hope this helps!
Also if there ears or ear is pointing tires you that is a clue that they are paying attention to you.
Just try to combinate different exercises and a lot of transitions.