Do different things to keep your horses’ mind active. Circles and workin on bend is great. You can use poles to lengthen or collect your horse. You can create a jumping course but lower the poles to the ground so you can work on your bend and turns, collection/extension, and distances. Raised cavaletti also make your horse work on lifting their legs. If you used raise cavaletti your horse can’t get bored/lazy. You can also work on lead changes.
Well, Lola used to do this and I realized she was getting bored. What I started doing was randomly queing her left or right. Or I'll suddenly ask for a half-pass. It caused her to be unsure of when I was going to que her. I also incorperated more trot poles amd would space them weird at times, so she would have to pay attention more to where her hooves where. If that doesn't work, I sometimes just had to bear through it, and just keep asking her forward!😂 Hope this helps!🙃