Start doing 4 X 1k @ 6:45/mile pace w/ 60s recovery once a week. Add an interval every few weeks, and then bump up the distance to a full mile. See if you can get it to 4 x mile @ 6:45 w/ 75-90s rest. Once you're there, see if you can start dropping a few seconds off the pace, maybe down to 6:30.
At the same time, start running an aerobic fartlek per week. If you're doing a six mile run, do something like 1 mile warm-up, 1-2-3-4-3-2-1 minutes at a pretty quick bu sustainable pace w/ 1 minute recovery. See if you can build this up to 2 x 12 minutes w/ 2 minutes recovery. You can even do this on the track every once in a while if you want to see how fast it's going: gun for just over 7:00 pace at first, and just under once you've got the intervals up to 8 minutes or longer (3 x 8 minutes w/ 2 mins rec).
Do a long run of 25% of your weekly mileage--for you, probably about 9-11 mpw. Do strides at the end of this run, as well as at the end of a couple other easy runs per week.