As a personal trainer and a running nerd I often get asked about running form. Although I do not claim to have the perfect form myself (I'm working on it) I do know the principles and I use them when I can.
First thing you want to remember is that running is more like a controlled forward fall, lean from your ankles about 10 degrees without bending at the waist (hold that core straight.)
Next you want your eyes gazing down at the road ahead of you. I like to look at other runners feet while racing to keep this position, be sure not to tuck your chin to your chest you want your head and neck nice and relaxed.
Breathing. This was a challenge for me when I first started running. I just couldn't figure out how to breathe right. Really the only trick to this is breathing through your mouth only and relax as much as you can and it will come naturally.
Most runners don't realize that your upper body also plays an important role in your form so let's look at the shoulders. You want your shoulders low and relaxed. To help you get the picture right now you should raise your shoulders toward your ears then let go. Which feels better? Low, of course, but most runners tend to tense up during runs and this tension is wasting energy that you can be using to run faster.
Arms: you'll want to hold your elbows in at a 90 degree angle with your forearms parallel to the ground, swing your arms forward and backward in a straight line and avoid swinging your arms across your body which will again slow you down. You want to drive your elbows straight back when you're picking up the pace with your hands reaching the side seam of your shorts.
Keep hands slightly cupped with thumb and index finger resting on each other and push down with your hands and elbows while in motion.
And now for everybodys favorite part, your feet!
Yes there are a few different type of strikers out there, heel, mid foot, and forefoot. Here's the skinny on each one.
Heel strikers can be injured if they land too far back on their heels because the position over flexes the foot but even more common is that heel striking can hurt your over all pace because you are literally breaking as you come down on your foot.
Forefoot strikers put extra stress on their calves which can cause a host of lower leg injuries.
What I think works best is to strike on the mid foot, it enhances stability through your stride and promotes more turnover so your feet stay on the ground for the least amount of time.
Changing your form takes time, I have been heel striking for some time and changing to mid foot is taking a lot of effort, but the better I become at it the better my race times become.