While out running with the club this morning I remembered a couple of other things to add...
Although I haven't read Chi Running, or gone into great depths with the biomechanics thing, I did read about some techniques somewhere a while ago that have worked for me
Running is not just about foot fall...it's about your whole body. I have learnt to concentrate on how I place my legs and basically you 'plant' your foot beneath your body, push through, and kick up at the back. The reasoning behind the three parts is
1. by 'planting your foot underneath your body you are not a) over stretching with your foot landing in front, which would be a heel strike and therefore a brake, or b) leaning too far forward making your foot land behind you, which would risk knee injuries due to the shock passing through it.
2. by pushing through you are naturally propelling yourself forward quite efficiently, and I found that it's quite easy to increase speed once this technique becomes natural
3. by kicking up at the back your leg is in the correct position to bring through efficiently and economically for the next step
So sometimes when I'm finding it tough I check in on how I'm running and tell myself "plant, push, and kick", which has never failed to help.
In my previous post I said about midfoot landing, there is one exception to this...which again I remembered this morning whilst climbing a hill! And of course that exception is when running up hills

Forefoot running is best going up hills, reverting to midfoot running down hills.
Another thing worth mentioning is posture. Your body should be reasonably upright at all times with your head up. I see so many runners, particularly when running up hills, with their head down looking at the ground. What you are actually doing when you run like this is restricting your airway, which is the worst thing you can do particularly when you need extra oxygen going up hills.
Finally, you should try and relax your upper body as much as you can because tense muscles actually weigh more, meaning your legs are working harder to carry the upper body through the run.
But like I say, I haven't studied biomechanics...it's just tips and techniques I've picked up along the way that have helped to improve my running.