You asked what "nuggets of wisdom" got me from 3:08 to 2:27. None of this will come as much of a suprise, but if I had done it all by myself I would have done too much too soon and got injured.
1. Think long range and work on developing your aerobic base by slowly building up your mileage base. You still need to build that lifetime base. However one advantage over people that did run in HS or college was I wasnt suffering the burnout factor that seemed pretty common in those runners.
2. Be consistent. Consistently putting in the miles is key. Running the 3:08 was off of a 50-60 miles a week. Running the 2:27 was after consistent 90-110 miles a week.
3. "If the marathon is your chosen distance, you need to focus on it at the expense of other distances". This was something one of my coaches said to me as I was trying to get faster in the 5K and 10K. The training was focused on running faster marathons not shorter stuff. Consequently my 5k and 10K PR's are no where near what the charts would say someone with a 2:27 PR should run. Crazy Jason Mayeroff I believe has said something similar.
3. Mix it up. Your training needs to change over time to work on areas that need to be developed and to keep things fresh. E.g. Lacking strength - empahsize hills.
When I hit that plateau of mid-2:30s, my current coach hooked me up with a different coach (who had a 2:18PR) and we shifted the training to more intervals given my lack of background of HS and college speedwork. We did longer intervals on Tuesdays, shorter on Thursdays, 4-6 mile tempo on Sat and Long Run on Sun. We did 3 week cycles that started with 6 x800 on Tuesdays and 6x400 on Thursday. Each week you added on more rep until you got to 8. If you could hold a consistent pace on this then you bumped up the distance of the intervals and started at 6 reps with them at the same pace as before. Otherwise if you struggled to hold the pace than you repeated the cycle. The goal was to get up to repeats of 2 miles at the same pace as the first cylce of 800s. Never got to that goal as only got up to 1 mile repeats before ran the 2:27. Of course the Sunday long run was key and as the training went along sections of it were run at marathon pace. Started with 3 miles and progressed to 12.
Ironically, after I ran the 2:27 I wanted to go to sub 2:22 and got injured because I failed to mention little pains to my coach and they grew to be bigger pains and then nagging injuries that lasted years.