Concrete footpaths and the like is absolutely the worst surface. You should run on the road itself where possible. Forest trails are the berries if you want some variety. Here in Atlanta there are tons of them. Running through trees can be exhilirating...creates that forest chase sensation and all that. Also it is a good idea to have a slightly bumpy surface every once in while to help the stability of the ankles.
The thing that has really revolutionised my running though is having a race to prepare for. I'm 35 and intend to do the half-marathon in a VERY modest 2:14/15. That works out at 10:15 miles. I'm not going to set the world on fire at that pace, but I'm going to finish my first half, which I think is crucial. The half in Atlanta is going to be quite hilly compared to Miami, and of course, the Bay Run from Glengariff to Bantry, is as a lot of city folk like to remind us, nothing but hills. My goal in all of these races given the increasing difficulty will be to finish. In the meantime, I'm going to give the Junior C hurling and Junior D football at least another year at the North American Championships, so after Miami, I going to work in some heavy speed intervals, fartlek, and 400's and 800's between February and May. I have also take to doing some corework/pilates this week. I can already feel the differance. Posture is everything.