Someone recently posted in the Runner's World online community for advice on stretching, and I, of course, had to throw in my two-cents worth. Considering I've only been running one year, two cents may be all it's worth! But it has been working for me so far! Of course, I've never been prone to injury luckily. I've played volleyball since I was 12 and had only two slight injuries (I'm 35 now). I never injured myself in my years of playing basketball. I have learned that running injuries are far different. They are less likely to be trauma and more likely to be from overuse. I did tweek both my achilles last year but they are both back to about 90%. Stretching, taking it easy on hills and speedwork for a while and calf-raises really helped my achilles (since I don't have insurance or the money to see a physician or a PT!).
With that intro, here's what I posted on my thoughts on stretching:
The consensus I have gotten from various trusted sources is the best time to stretch is when your muscles are warm. That means, if stretching before a run, walk or slow jog for about 10ish minutes first, then stop and stretch, then start your training run. After a run, cool down with another 10ish minutes of slow jogging/walking and stretch again.
Armed with that advice, I still only stretch AFTER a run but it has reduced sore muscles CONSIDERABLY and helped a nagging achilles injury (mentioned above) to heal.
Before a shorter distance race (5 or 10K), I'll warm up by running slowly for about 10 minutes pre-race. For the 5K, I might even recruit some fast twitch muscles by throwing in some short bursts of faster running to warm up. (I say "might" because I haven't done a 5K yet (haha!), but that's my plan for when I do!) For longer races, I let the first few miles of the race itself be my warm-up.