i love justin...jogs the first three and kills a 300. i'm not sure i've ever broke 40, even in workouts.
so back in the "heyday," rubio just made it simple for me. starting out small, building up.
15x200 w/ 200jog> 20x200 w 200jog (quicker jog this time)
then 3x4x300 w/ 100jog/3min on sets> 3x5x300 (same rec)>4x4x300
then 8x400 w/ 1min> 10x400> 12x400
then 5x600> 8x600
only one time did i ever get to do the 4x800, and i couldn't even finish. it was on my trip to Wisco, a bit windy. hit 1:59, 1:59, 59 and stopped. 4min between, halfway through the 3rd one i chickened out and turned the last 2 into 4x400 w/ 75s rec. still averaged sub 60 for everything, ran 3:40 two weeks later.
basically when i could handle approx 3.6-4.4k worth of work (in NO LESS than 400m increments), w/ short rest, I knew i was in sub 4 shape. of course we were also sprinkling hill reps, tempos, mile reps, the occasional 14x400 at 5k pace (gosh i loved those days, felt so easy compared to mile pace!)
pretty simple really. biggest thing, IMO, is picking a plan/progression and sticking with it. you CAN'T come on here and "pick and choose" from what sounds "good" or "fun." you'll will nearly always find the greatest chance of success with starting at a certain point (like your CURRENT fitness, NOT your goal fitness) and progressing in realistic increments. Rubio had me start right close to 60 pace (i think he allowed the first few to be 31s/46-47s as we started out w/ short, easy workouts) but remember that sometimes we'd start with as little as 12x200m.....yeah, that's stupid simple, anyone can do that, but 5mos down the road, i'm going 10x400 @58-59, 4x(600 @90, 100jog, 300 @42), 4xMi @ 4:25, etc......
best of luck buddy.
cheers, dude-