One key to successful running is to run lots of miles and to stay healthy. To accomplish this much of your running has to be done at an easy pace. 1-2 taxing efforts a week is all that is needed to improve your running, but only if you have a sufficient amount of weekly/monthly miles. The time spent running has a direct correlation to your fitness and running performance.
On all of my runs I start off easy, even on a hard workout day. I usually need 10-15 minutes of slower, easy running to get my muscles warmed up before I start on the hard stuff. On my recovery days I run all of the run at a slower pace, usually 2 minutes a mile or slower than my race pace for a 10k. One of the most common mistakes runners make is being a slave to their GPS, trying to maintain a pace. I don't use a GPS, I go on what my perceived effort is. My pace for an easy effort days varies quite a bit depending on how rested or how tired I am. It does not matter, if it feels easy, then you are accomplishing what youset out to do. If it feels hard, you need to slow down. Relax, focus on finding a comfortable stride by working on your running form.