I agree with the above posts in regards to getting a trainer to assist. It is an important skill to have, but very hard to teach it on your own.
Lunge is good and it allows the rider to see the horses free movement, good to spot injury or to exercise without being on top. Ground manners are very important when dealing with horses, as like you said before, they can turn on you if you don't have the knowledge to send them in another direction.
A few tips I have would be to always keep the line taught, slack in the line can cause a tripping hazard to you, as well as the horse does not have any sort of contact on his face, which is important because you need to have control.
I always try and stand at the shoulder line (much like when just leading) and not let the horse go to forward, or slug behind. I also move my feet quite a bit, but not in a huge circle, they stay at one spot and I just turn around.
I also make a V shape with the whip and lunge line, and always trail the whip behind but never use it. It acts a reassurance so the horse knows that he is working. By creating a V with the line, it almost makes a box around the horse, where you have control. If hes too slow you can bring the whip a little closer and if he's to forward then you can move the whip back to let him relax.
When I familiarize horses with whips I start very slow, keep the whip on the ground and allow the horse to walk by it many times, then gently pick it up but always hold it a little bit behind you so he doesn't get startled. Once he is more comfortable with the whip, then you can start to fully pick it up. I rub it on the horses legs to begin and once you are able to touch all of his legs with the whip then I would move up to his side, and eventually over his back and his head. By touching him with the whip I mean literally just rubbing the whip over his body. Once he learns it is not a weapon he will learn to trust it more, thus allowing him to work calmly with the whip in his presence.
Hopefully some of these tips help you as they have helped me :)