Run Faster from the 5K to the Marathon: How to be your own coach by Brad Hudson
Says running at a lot of different speeds and intensities is really important. Basic types are hills/hill sprints, tempo/threshold runs (hard for 2 to 6 miles), intervals, and slower longer runs. I basically have been doing only intervals. Trying to do all these others at least once a week, and slower easier runs as often as I can manage with my 15 hour grueling workdays.

Today I did 2 miles in 14:29, then two easy miles and finally 2 more miles (somewhat uphill) in 16:09. My low intense/high freq strength training is consisting of a set of overhead presses, closee grip bench presses, tri pushdowns and a set of chinups. Very low intensity. Very afraid of insomnia.