Hip extension
Hip extension is perhaps the most important aspect of proper running form, but it's the component that's frequently overlooked and/or misunderstood.
Hip extension begins as your foot contacts the ground, ideally directly under your body, continues as you pull the leg beneath you, and ends right before you push off with your ankle. Your speed depends on how much power you use to drive your hip back.
The driving phase of hip extension is brief and shouldn't be confused with forcing the leg backwards. Once you've initiated the drive and generated power through the hip, you should relax and let the leg travel behind you naturally. The distance or degree to which your leg travels depends on the force generated during the driving phase. Therefore, there's no reason to force the leg backwards.
Instead, focus on increasing mobility in your hip flexors—which provide the needed flexibility to generate proper extension—and strengthen your hips, glutes and hamstrings. Here's an effective routine for improving hip extension.
More: 5 Hip Strengthening Exercises
Footstrike and Cadence
Despite the emphasis on footstrike, trying to change the way your feet hit the ground is actually a flawed concept. Instead, focus on where your foot lands in relation to your center of mass.
For example, many people believe that a heel strike is incorrect form, but research studies have shown that the heel strike itself is not inherently bad. Rather, it's the fact that typically, heel striking is the result of the lead leg landing too far out in front of your body. This is called overstriding.
Studies have shown that as long as your foot lands under your center of mass, the way that your foot strikes the ground (heel, forefoot, midfoot) does not affect impact loading rates, injury risk or efficiency. Therefore, rather than focusing on your footstrike alone, work to improve your cadence to prevent overstriding.