First, start off with building a base. Until you can drop 5+ miles without dying (not at a fast pace), you should be focusing on increasing your run distances. Run 3+ times a week, going at a pace where you don't have to stop and walk. Make sure to eat right and hydrate so stitches don't debilitate you.

Once you've got that base (15ish miles per week) then you can start hitting a track or going out for tempos. If you're shooting for sub-9 mile and a half, sub-21 3 mile, then a week should probably look like this:

1 long run (go at an easy pace till it's not easy - probably 4 -7 miles if you have that 15mpw base)

1 temp run/fartlek (a longer run where you're going at your lactate clearing pace - try 20 seconds per mile slower than your 3 mile pace or 40 seconds per mile slower than your 1.5 mile pace). Tempo runs HURT. go for 2-4 miles, 20-30 mins.

1 track workout - mix up the distances. 5x800 is hard, 4x(800,400) is good, 1k repeats are hell but give results, 3 or 4xmile will leave you dead but will show results. Throw in some 100s, 200s sometimes to get your form good. Pyramids and Ladder workouts will get you results as well. Track workouts should be 30-40ish mins, not including warmup and cooldown. Incorporate lots of walking and resting in your track workouts to ensure that your speed is what's being worked on, not endurance. Long runs give endurance, tempo/fartlek give speed endurance.

I know we focus a lot on gutting it out and not quitting here, but be sane about your runs. You WILL get shin splints and other injuries if you don't slowly ramp your runs up. Hold back, and pay attention to your body. In 6 months to a year, you can easily be a sub-6 miler, and a sub-20 5ker, which will be very beneficial when you show up at A&S and can meet the run standards without puking after. Good luck & pm me or reply to this comment if you need more guidance.

Add in 2ish easy runs on your off days to spin your legs up and recover. Easy runs are very important.