How can I improve?

Get stronger, lighten your bike. Those are the basic premises for bunny hopping

There’s something to be said for refining technique, but that will only get you so far (high).

Find something that is juuuuust too high for you to clear/hop up onto. Then just work at it. Eventually you’ll get it. Then pick something a little taller

It’s just gonna come.down to reps making you stronger at the end of the day, just like a baseball player training in the batting cages to improve their swing, weight lifters putting in hours to add weight, or a swimmer doing laps for endurance.