I had never ran before and didn't do summer conditioning. I ran 18:15 as my first 5k race with about 2 weeks of training. Finished my cross season with a PR of 17:11 and didn't run more than 30 mpw. Over the winter, I did all easy paced miles except for my threshold run. Took it slow to begin with, ~35-40 mpw, and I felt fantastic. Upped it to about 55-60 mpw after a 6 week build up and got a solid 2 months of high mileage training. Showed up to track this year in the greatest shape of my life. I ran the 1600 only 2 times, and my first race was a 4:51. Most recently, I ran 4:47. I also ran the 800 and 3200 in 2:08 and 10:19.
My summer plan is to build up to about 60 mpw again. I am doing a 6 week cycle that basically alternates each week with hill repeats, easy speed, and a one hour fartlek. I am increasing my long run from 70 minutes to 90. The biggest aerobic gains I believe will come from increasing my threshold. I have begun doing a strategy that my coach taught me: Starting out with 4 x mile at threshold pace, then doing a 4 mile threshold at the same pace the next week. Continuing to increase by doing 5 x mile, then a 5 mile threshold, etc.