I only trail run. I cannot stand being on the road. If you take the advice that has been given here, I think you will do just fine. Start slowly, walk/run, stretch, good shoes....

Like Yellow said, I only run for time. The terrain varies so much that worry about "pace" does not work. I train that way, and I do just fine in races.

and enjoy, it is a whole different animal than being on the road.