The second of the two issues with my running form was my posture. With the number of years I have spent in front of a computer I have developed a somewhat hunched-over posture, which I naturally carried over to my running.
The first thing I had to do was stop looking at the ground. Focusing on each step makes for a very long, tiring run and all I can see and think about is my feet and my legs, as well as being unaware of any potential safety hazards ahead of me. I broke myself of the habit by constantly reminding myself to look forward at the horizon when running, or by picking something in the distance and looking at it.
Next was to straighten up. Keeping a straight spine and square shoulders, as well as pushing my chest out a little allowed me to run longer without the back pain I had been feeling initially towards the end of my runs, it also allowed for easier breathing, which is the next part. Like all posture adjustments, this will take a lot of reminding yourself, but it does become natural over time.
More on running form and posture.
One of the problems I ran in to was side stitches, and I found two things to help me fix that. First, was to try to exhale as much as I could, reasonably, with each breath. Second, was to force my breath cycle (in/out) to take an odd number of steps. For me, I settled on two in, three out but that is just a guideline. If you are constantly breathing in with every right step it can cause side stitches. You will have to constantly remind yourself of this at first, but it becomes natural after a few runs.
More on side stitches, and how to fix them.
