Like your pronating ankle and hyperextended knees.  Hyperextension in the knees comes from  pushing back rather than lifting up in your positions (like 5th position many try to push back into the knees rather than pull up through the pelvis - two completely different ways of thinking to accomplish 5th position).  If you do a plie in 5th and dont come back up to a centered standing position while feeling "boyant" and slight stretch it is probably executed improperly.  Similarly it is difficult to train one to get the proper zippering of the inner thigh muscles to keep from pushing back in the knees.

But it is a whole aesthetic.  Extending through the top of the head, relaxed shoulders with an open chest.  Stretch in your arms port de bras. Engaged abdominals with a closed lower rib cage.  A centered pelvis, stretch in the front part of the thighs, engaged rotator muscles, relaxed/lengthened knees, right down to the foot (and many more little details I skipped here).  But you can get the idea of how one thing fits to another.  I had a problem with balance on eleve for a couple weeks now until my instructor said, "its your arms".  We spent a few minutes after class and bingo, my eleve is solid and maintainable once again.  Silly how these little details can bring you over the top.  I have found it is the whole body aware thing.

I would also expect you have a weak transverse abdominal muscle (most every dancer does).  Have you ever done pilates?  Might be good to try.  Will also teach your body how to breathe properly and deeply with your abdominals and transverse abdominal engaged.  Will really help your dancing in both subliminal and conscious ways.

HAve fun.  It is an unforgiving artform I know, but when things zipper even for a moment it is a great experience as I am sure you are aware.

~Ron.