I have quite a few.
I think my worst is holding onto the left rein, my instructor is always teling me to release the left one, Im improving though I think
I also draw my heels up when I need to ask more with my leg
I turn my elbows out and swing my leg backwards over a jump but that is beginning to improve (This one never used to be a problem till I had a break from it between retiring one horse and backing/bringing on the next one to the stage where we could start jumping)
Flatwork wise i lean to the right and drop my right shoulder.... bad habit picked up from my polo playing days!
Jumping wise... apprently looking at the floor is far better than looking where you are going! Again i look over the right shoulder and usually at the bottom of the fence on approach so another one picked up from my polo playing days!
Polo was great fun it just trashed my classical riding position!!! And the worst part is i can blame the polo as i never used to do it!!
Hunched shoulders My instructor used to nag constantly then one day I saw a demo by Carl 'beautiful shoulders' Hester and it was like a light bulb moment!! I wish I had his shoulders! (along with the rest of his ability of course!)
Collapsing my position and tipping forward in canter transitions. Poor horse. I'm trying to get super strict with myself before asking for the transition.
Hmmm - where to start?! Washing line reins definitely #1. Forgetting to breathe whilst jumping in an arena #2. Stopping there - it's getting too depressing. Fortunately, I have regular lessons with an excellent instructor, and a loop tape of her instructions in my head!
Hunching forwards, not sitting up enough and shoulders back - my body just naturally won't do it. Looking down is another big fault of mine as is keeping my hands too low. In fact I can't think of much good! I think my lower leg is ok...
I'm doing pilates for equestrians classes to try and sort myself out once and for all!
Leaning forward, turning my thumbs down like holding a shopping trolley, heels up, looking down, hold breath whenever I canter.... there's more but that'll do! Years of lessons and go through stages of getting it right then loosing it again!
Crushing my neck down like a tortoise and hanging my mouth open. It's my "thinking face". And yes, it is as ghastly as it sounds. On the other hand, it gives me opportunity to ride around squeaking "JOLLY TALL! Channel your inner giraffe!"
At the moment, the one I'm still battling with - my naughty elbows that won't stay back and down. They just float off into space and I creep up my reins. I'm working with my instructor on this, and imagining weight in my elbows which works for me but takes a lot on concentration!
Sticking my feet forward in the 'emergency brace position' in canter/gallop. Defensive move learned back when I had Brave the psycho bucker. Ugly, but surprisingly effective, even bareback.