I recently completed my first 10k race. My time was 55:09.6. Not exactly an olympian effort, but I learned a few things. And besides, I'm 39 years old, and really don't know why I suddenly fell love with long distance running in the first place. The biggest mistake I made was in training the week prior to the race. I ran twice, and did one weight training sessions. What I think I should've been doing was yoga, tai chi, stretching and walking, while concentrating on eating clean and low calorie to drop a few extra pounds.
Some friends asked me to do the running portion of a team amateur triathlon event the following week. So I didn't run during the week leading up to it, did lots of yoga, tai chi, and stretching, and ate as clean as I could (given I was exhausted and burnt from the 10k still.) Anyhow, on race day I ran 4.3 miles in 34:04. Getting enough rest and nutrition is just as vital as the exercise portion of training. It's tough to remember, even for somebody like me, who says it all the damn time.
When I run, I concentrate on making each step as light as possible, and I focus on the time when neither foot is touching the ground. After a couple miles I start to get light headed, and feel like I'm flying, drifting on the wind. I'm a big fan of swinging your arms. The added momentum feels good to me, however I've learned over the years that you can conserve energy by keeping your hands below heart level. When they rise higher than the heart, it has to work much harder; good for power-walking, not so good for racing.