1) Torso twisting - excessive rotation of the torso while running is a waste of your precious energy.Imagine a line drawn down the front of your body right in the middle. Your hands should never cross that line. Rather, imagine you are x-country skiing. That is the action you want - a nice front to back motion
2) Long Loping Strides - Don't be a "Loping Laura!" Avoid this style of running as it leads to other problems: (see #3-#7)
3) Heel Striking - once the norm, popular opinion now favours a "mid-foot" strike, as this will ensure that your foot is landing under your hip, not out in front of your body. Why is that important? See #4...
4) Foot landing in front of body - every time this happens you are essentially putting on the brakes. Even worse, you are creating a lot of force that will travel up your body, affecting ankle, knees and hips.
5) Slow cadence - cadence refers to the total number of 'revolutions per minute' (RPM), or number of full cycles taken within a minute. A slow cadence equals slow speeds, and it also forces you into heel striking which leads to braking and higher impact forces. Yuck! Who wants that?
6) Bending at waist - this is a common problem for newish runners. Avoid this at all costs! Focus on leaning forward from the ankles when you run, keeping your body straight. Go on YouTube and watch the 1500 Metre race from the last Olympics. See anyone bending at the waist?
7) Running with tension - loosen up! This is your time to decompress... Relax your shoulders, unclench those fists. Let the day go. When you run relaxed you run farther while using less of that precious energy
8) Run lightly - Our ancestors relied on running quickly and quietly. While you may not be running as a means of putting food on your family's table tonight, you will still benefit from practicing to run making as little sound as possible. This will help you adopt an efficient running stride that avoids many of the pitfalls mentioned above
9) Keep the knee soft - a common mistake is to completely straighten the leg just before the foot contacts the ground. Instead, keep the knee bent before contact
We are all different, and our individual running styles reflect this. I can pick out most of my running friend from a long way off, just by paying attention to their particular quirks. You can certainly fix problems that exist, but you are ultimately designed to have your own identifying characteristics. I say this so that you don't get to hung up on trying to look like the people running beside you. Embrace your differences! But also work hard to fix the bad habits you may have picked up. Everything works itself out in the end!