Hello! Poles before and after the fence helps. You can do a jump, with 5 poles after with one stride in between each pole. This will teach them to be aware of where they put their feet and they can’t rush. Also doing a line with a pole in the middle. Lots of transitions. In a line transition to a halt before the fence. Circle and then go back to the second part of the line. Or in a line you can alternate between 5/6 strides or put a 7 in a 5 stride with poles to really get them listening. But most importantly in the beginning of your ride do a lot of trot/walk, canter forward, half transitions and full transitions down to trot. If you just do just downward transitions and no forward ones, they won’t listen as well when they’re forward
You should slow your thoughts down. What’s probably happening is that you think “oh my goodness, now she’s going to do this and this etc..”
Another thing you should do is soften your eyes, when you squint your eyes your whole body tenses and causes the horse to become blocked by you either moving too much or too little.
A good exercise is a bunch of very small vertices set up in a clover pattern, maybe on the inside of a twenty metre circle.