I'm using a Tinman plan which worked very well for me and got me from 20:00 5k to 17:00 5k in 14 months. After the first few months, which I spent to increase my volume from 2 days a week to 5-6 days a week, a typical week was like this:
mo: long run 90 min easy ~8:00 pace with strides
tu: off
we: CV workout, 5-6x1000m in 3:25 & 5x200 from 35 (mile) down to 30 (800)
thursday - 5 mile recovery run, 8:30/mi
friday - 8 mile run, ~8:00 with hill sprints
saturday - 4-6 mile tempo run, around 6 min pace (MP). then 4x400 in 70 or 200s or hill sprints
sunday - 5-8 mile run, 8:00
Since 2 weeks I started to replace the Tempo with either a race (submaximal, first 80% at threshold then good finish), or a harder session. I'm building from 12x400 in 5:05/76s pace to 8x600 to 6x800 to 5x1000 to 3xMile all at same pace. Does this make sense? Or is this too intense and I should keep the tempo runs.
I'm very strong anaerobically (400, 800, kick in races, short intervals) and need to improve my aerobic system. 5:05 feels aerobic to me, at least when I did the 400s but I'm afraid to shift more towards anaerobic with these workouts and stop improving my threshold and aerobic base, which is what increased my race times the most so far.
Mileage is currently 50 mpw, I plan to increase it to 55-60 mpw but at 70 mpw I got injured in the foot so I need to take it slowly.