Kitana
You have to stay out of the air, I had this problem before, remember teleporting after any jump will drop you towards the ground; I suggest you don't use skydrop that much (saying this just in case if it contributed to your problem). I punish kitana with trance evertime she recovers by landing from her air attacks. You should anticipate her fan lift wake-up and trance afterwards from a proper range. Her combos reach a strong level of distance, they consist of medium hits most of the time, if you back up enough to keep away, remember to f1,2 as she recovers (whether you jump over her or evade her fan slashes), it has great range, so does B2,1. If she persistently pressures with block strings, uppercut before she dashes into another one, Quan Chi has the best uppercut in her hands.
Mileena
All you have to do is anticipate her wake up attacks (bait tactics), the roll and tricky teleports. If a mileena tries to mix up by landing another overhead after you block the first one, jump kick into sky drop. She has a low hit combo as well, just tap low on block so your gaurd can switch to low than high immediately. punish with B3,1+2 more often and follow up with a trance link, you cant afford Mileena to escape you grasp, she is hard for Chi to catch. Only use skull throw (enhanced) when she is caught by trance, it is pretty safe, but slow, remember Mileena only needs to teleport to put a halt on your zoning tactics.
I cannot explain the best strategy to fight Kung Lao without going into serious details, I'm working on a vid that emphasizes Quan Chi's most difficult matchups, Kung Lao is one of them. I will have it up soon, sometime next week. I hope that my advice will get you somewhere with those two matchups, remember that Quan Chi is more on the lower end of the roster's balanced characters, its takes a bit more effort than simply having fun with him to win against tougher players/characters.