I do 4 miles 3 days a week. I plan on working my way up to 6 miles then stopping distance increasing and working solely on improving my time in the 6 mile. Come summer time though ill probably start doing sprints. Its way too cold to do sprints in the winter in the middle of illinois when its usually like 25 degrees.
I'm not trying to tell you to leave or anything, but you should go to a running board if you have running questions. They will have a lot more expertise on that.