Move your hips forward :)
This is my worst habit! Ok so basically my trainer always tells me to tuck my butt under myself- kind of like you are sitting ontop of yourself- and lift your pelvis up through your hands(not all the way through your hands but you get what I mean)
try riding one handed (with both reins in one hand) and place your forearm against your lower back so you can realize when you arch. another tip is to roll your pelvis foreword to keep your spine straight and not flexed
Imagine what you want your back to look like (flat) and push your belly button towards your spine. My dressage trainer tells me to imagine that a straight metal rod is running through your back so that your head, shoulders, back and seat bones are all in a straight line 😊
Tighten your abs but not your back
Find your seat bones against the saddle and focus on keeping their back points underneath you.
Tuck your pelvis underneath yourself and keep your shoulders back, hopefully this helps!
this is kind of weird but it works, suck your belly button into your spine:)