Turnout, turnout, turnout, and more turnout.
If you can’t/won’t change that, make sure your warm up is adequately addressing the needs of your horse. I have seen riders rush through their warm up to get to the fun stuff (jumping). If your horse needs 25 minutes of walking with figures, it needs 25 minutes of walking even if it seems boring to the rider.
My mare is 17, out about 22 hours a day, in to eat only, weather pending. She’s on twice yearly Adequan and warms up better with walking, then a short trot, then some canter, then back to serious trot work.