I can give you some suggestions :
The opener : Try this : Contract abs, relax both arms (shoulders, elbows, pecs) then try to start your run from that. You can try keeping your hips holded until you have a good position or relax them, for arms, give the move you want.
Through the Youtube run, you have always the same body position and to the same kind of paths. By changing your opener you can make more variety of runs.
If you try some different styles of openers, you will be more used to restart a random opener from any position and its really helpfull in parkour.
The position of your body is really an important point. More he is horizontal (falling in front of you) more you take speed. If you raise your body vertically you will lose speed.
When you do a step, relax your knees, of course, but try to hold them to avoid through relaxing they contract too much, that allow to do smaller steps to keep a strong balance.
For arms, I generally relax my shoulders, but I hold them when they go too high. If I need speed I raise the shoulder on the side where the hip is extended. For pec, of course arms and legs are asymmetrics, generally I use only one pec, the other is relaxed and I change when I do a step.
For turning : Give your weight on the side where you want to go. You can use your lateral joints (lumbars and glutes) and the chest. Look at the position of the next foot touching the ground : he has to touch the ground in the direction where you want to go in.
I hope that could help you. Don't forget the best way to learn is still training ;)
Last edited by Mocucha; Nov 16, 2013 at 11:55 PM.