I would suggest attempting to rework the balance and flow before attempting to improve on anything else, a specific example of a problem with balance is after uke's run has finished. Your best bet with balance issues is messing around with foot/knee positions from what I've experienced, and using your hands can work in some cases (e.g. a spinning kick where you use your hand for extra momentum) but don't rely on them too much, as they can make a spar look messy.
I never really focus on being realistic, but more rather stylish. With jumps, from my own experience, experimenting with shoulder ankle and glute movements in specific positions can give you a shittonne of momentum to perform jumps and spins, which makes everything look more flashy, a perfect position for a jump was your tori early into the game, but jumping isn't exactly required in a spar.
As for flow, just try and make everything go together, personally, I look at most spars I do every few frames to see if everything's flowing together correctly, but I would also suggest looking how each joint follows through when relaxed and just go from there (There are some cases where you can kind of get away with sharp twists)
If you need me to explain more/give examples of your stuff or other people's stuff that I think flows well with images just ask.