Stretch a lot afterwards... whilst you are still warm. Absolutely essential. But not before. I like running as early as possibly in the day too. Just because of the light and the lack of traffic
I spent last week running after having not run since December. Maybe it's because I haven't been doing as much serious cycling this year that I found it easier than expected. So I did 4 miles on Monday, 5 on Tuesday, 6 on Wednesday, 8 on Thursday, then had a break and did 12 on Saturday. My legs were fine but it was the impact on my feet that did bad things - very sore tendons or ligaments (I am not sure which!). Still, they recovered pretty quickly... and I've been back on the bike today.
I have been seriously thinking about working up to doing a half ironman, or maybe, eventually, even a full one. Can't be arsed with normal triathalon as I am just not fast as a runner or swimmer - the longer, endurance things suit me better. Basically, I have only one running pace, which I can keep up for anything from 2 to 12 miles (maybe more, I don't know) without any real problem.