I used to never really warm up, I'd just start out a little slower and then pick up the pace.
These days, I usually start with a walk. At my age I seem to wake up creaky and a bit achey no matter what I did the day before, so the walk help get everything back in working order. After about a quarter mile I'll start to jog, and then it depends on what the run's objective is from there.
I do a bit of stretching afterwards, but I am not religious about it. I do, however, do yoga 2 or 3 times a week, independently of the runs.
2.5 years, 45 pounds later... 128ish pounds