I was a distance runner in high school... first off, foot strike does make a difference. Your midfoot or ball of the foot should strike, just before your heel, technically speaking. But just run, if you do it long enough, your body will "train" itself. Dont lean back going downhill, it's harder on your ankles and dosn't let gravity help you down the hill; lean into the downhills slightly. If you want to run faster than 7 minute miles, mix long slow distance runs (3-5 miles) with short interval training (running the straights and jogging the curves on an outdoor track for 2 miles or 8x400 meter laps). Also have one "short run" day; a two mile jog, slow and easy. Get tons of sleep, alternate lifting and running, and if you notice a "plateau" in performance, you are probably working too hard or not resting enough. Also, on the distance runs... if you cant carry on a conversation because you are breathing too hard, your going too fast (at least when you are starting out).
WATER...drink tons of water, and try to eat high protien and carbs within 30-45 minutes of working out.
In my peak days, I ran 45-70 miles a week, lifted (squats, abs, light chest and arms+ pushups and situps) and could out squat most of the football players on the team, though they weighed twice as much as me. I ran under 5 minute miles, and under 16 minutes for the 5k/3mile. My heart rate was somewhere around 48 BPM...(those were the days)
Get some good running shoes too... x-trainers will leave ya hurt. PM me if you'd like a few ideas to mix the training up... I've done just about all of it, though I admit I'm out of shape right now [beer]