When I run on the trail behind my house, I often see other runners heading in the opposite direction. I've started to give them "high five". It's motivating to me, and most of them smile at me and seem to pick up their own pace as well.
When running, and getting to a place where you feel you can't run any further, look for a spot 15 to 20 feet ahead of where you want to stop, and run to that spot. Then each time you run, run 15 to 20 feet PAST the spot you chose the run before.