You need to do flatwork you are not going to get anywhere without flatwork you are not going to get better by just jumping I am a jumper so we go fast and I go to international completions and once I was doing the FEI children’s classics lost my stirrups half way though and because of flatwork without stirrups and learning to jump without stirrups I came 5 out of 15 so you need flatwork to become better ask any professional rider and ask if they just do jumping.
If you already know how to do it, the only tip I can really give you is just ti be super aware of it, keep reminding your self you need to sit down or have a trainer/friend by the ring to keep reminding you of it. And remeber to relax otherwise it can be difficult to sit deep in the saddle
I would lengthen the stirrups a little bit. Ride a lot of transitions between trot and canter so you can try to take the seat from trot to canter. Think about to have your butt always in contact with the back part of the saddle. Do not push an squeeze your Seat forward downwards into the shoulder.
I'm a hunter. I need my stirrups to jump. The problem I'm having with this horse is when we're jumping. She's very lazy on the flat. But when we jump, she's a speedball lol. So I need my stirrups. Any tips now that you know that?
Start without stirrups and that will force you sit in your saddle. After your comfortable doing that use a dressage saddle if you have access to one and lengthen your stirrups don’t ride with short stirrups if you want to sit in the saddle. If you can’t get a dressage saddle try and find an deep saddle so not a flat one.