Do not brake every time your feet hit the ground. If you hear "scuffing" every time your feet hit the ground, that is essentially braking yourself and slowing down. Aim for a near silent footfall. Achieve this by increasing your cadence. Ideal cadence for most is 80-100 per minute. Top marathoners barely strike the ground.
Run fast. Often. To get faster, do short sprints and if those are not feasible, then run up hills. Running up hills will make you faster and stronger on the flats. Sprint intervals are also a great way to increase running's already high caloric burn.
Have great form. There is not too much action above your waist. There is hardly any mid-line crossing of your arms. Arms are perpendicular and rock back and forth. In sprints and hills, an aggressive pumping of arms will help propel the runner forward. Try not to bounce up and down overly (vertical oscillation.) Every action of your body is serving to propel you forward, not side to side or up and down. I have noticed countless runners literally moving from side to side with each stride, which is not serving to propel them forward.
Do not carry much extra weight .. Reconsider the gear that you're bringing along. Even 5-10lbs. less to carry around can make a huge difference in speed. There is no need to carry a pack or 3 water bottles on a short run. Look at your caloric intake. Most human glycogen stores are good or 90 minutes of activity. Less is more!
Ditch the gadgets. Watches are useful but phones and iPods have become quite distractions for the focused, fast runner. Take in the sounds of your environment. Hear your rapid breath. Dig the hoot of an owl calling at your local trail system as twilight sets in.
Do not fall prey to fads. The human foot does not need support and is a perfect anatomical feature on its own. Shoes with many "corrective features" and extra padding only serve to get in the way of excellent form. If your feet hurt, consider doing cross-training on a bicycle or running on trails. Slowly build up running distance and strengthen your feet rather than letting your feet stay weak in "shoe coffins."
Run on different surfaces. Trail running increases strength and helps build ankle tendons and muscles. Running through the woods can also be incredibly therapeutic. Run on sand at the beach for an extra tough challenge that will get your heart pumping
Run efficiently. In the beginning, it is common to need some kind of nutrition after 45 minutes or so. Sometimes, it is possible for some runners a half-marathon on a good breakfast and minimal fueling. The body will become more efficient over time and efficiency = economy. Running economy will allow you to go further and faster with less. An economic runner has no wasted movement and nearly all movement is dedicated to moving forward. Imagine trying to balance a glass of water on your head as you run. Keep it calm. Minimize grimacing of the face! Breathe easy. Even more so, over time your body will begin to burn fat for energy as it learns to become more efficient.
Have fun! If your wife, husband, or friend challenges you to a parking lot sprint after you've just ran 10 miles on the trail, take them up on it! You'll enjoy the competition and both of you will most likely have huge grins on your faces when you're done. Running takes us back to being a kid when we run through care through fields, neighborhoods and parks, for the fun of it.