What part? My seat used to be very bad, and my arms used to flat about like chicken wings! Lots of practices, leaning back, and focusing on pushing into hthe saddle has helped amazingly! It's hard with new/bigger horses, but bareback work is fantastic and has brought my riding on so much!
If it's something with the horses canter, focusing on getting the right lead on corners, and using impulsion!
I ride English style so this may be different for western riders 😊
God luck, practice, practice, practice!