How to correct my mechanics

I am trying to get more hip torso separation, land on the ball of my landing foot, and lead with my hips. Any tips or suggestions as how to go about correcting all of these issues. Should I try to correct them in a certain order or all at once? Do towel drills or do other drills?

What you really want to do is get the whole body involved in the process. I remember when I was a kid and I would go to the original Yankee Stadium every chance I got. I watched the pitchers, and I saw that the Yankees’ Big Three rotation—Allie Reynolds, Vic Raschi and Ed Lopat—were all doing the same thing: they were driving off the lower half of the body, using the legs, the hips and the torso in one continuous motion, and that was how they were generating the power behind their pitches, taking a lot of pressure off the arm and shoulder in the process. And yes, they all landed on the ball of the foot.
This website has a good number of drills you can do, including the one known as the Hershiser drill which aims to get the hips fully involved in the process. If you can work on these various aspects of the windup and delivery of the pitch you’ll be able to accomplish your objective. You can work on each phase separately and then put them all together, the way one assembles a jigsaw puzzle! So go ahead, give it a shot. 8)

No, towel drills are not for this, work on keeping your weight back as you are coming down to the front leg, then transferring forward as you snap the hips then throw. You do not have to be on the back leg, though. Just make sure you are either behind the mid-point(middle of stride) before the leg drives the hips. Players that lean too far back can have problems and you just want to be back enough to absorb and snap the front leg driving the hips and be coming forward at that hip snap point. Not having released the ball. Secondly, the landing is a heel to toe transfer that is soft, and kind of rolls and as you keep your weight back it can lead to a smoother transfer to the front, but think of it as stepping on a gas pedal. Try keeping your toe pointed at 3rd base dugout as you step then pointing it as you land. This keeps the hips closed until landing. Towel drills are good for those kids who need to learn how to get their body moving toward home without dropping it out too early, it can also be used for showing a pitcher to snap a throw. Some use it for different purposes, though. If you use the front leg effectively to drive the hips, it will force you into a follow through motion, bending and releasing. I actually do work on the front leg with the towel drill trying to get a release in sync with the front leg stiffening.
Hope this helps.