A book I've mentioned before, Lore of Running, dedicates an entire chapter to the contributions of Arthur Newton, who raced in the 1920's and 30's. Newton was what we would call today an ultra-marathoner. He ran a large number of races between 60-100 miles - but, his ideas helped to modernize training for all distance runners. In Lore of Running, Tim Noakes identifies 9 "rules" of Newton's training that have have become "common sense" in long distance training.
1) Train frequently year-round: Before Newton most world class runners trained only part of the year - and not very strenuously by today's standards. In fact many books of the time suggested walking as good training.
2) Start Gradually and Train Gently: Since many runners didn't train all year long - they tried to get back into training too quickly. Newton praised the benefits of what we would now call long slow distance (LSD). Which Noakes defines as 20-25% slower than race pace.
3) Train first for distance (only later for speed): I would say that's the major feature of my training for Boston. I'll be doing quite a bit of distance before I ever hit the track.
4) Don't set a daily schedule: Well, I've kind of messed up on this one. My days are scheduled for the next 25 weeks. However, I know I need to be flexible. If something comes up or I'm too tired or the weather is crazy on a "quality" day - I have no problem postponing the workout.
5) Don't race when you are training, and run time trials and races longer than 16 km only infrequently: This basically relates to the idea of "periodization" discussed earlier. Set aside a good chunk of time that's just for training - not racing. Now, his idea of "infrequently" is a little different than mine. He suggested that marathoners should not race more frequently than every two months - running a marathon about every 2 years is enough for me!
6) Specialize: Noakes interprets this as make sure that you train for a specific distance. Training for a 5k is very different than training for a marathon. Another way to think about it is to concentrate on the distance that you are most talented at - although, i'll admit that if that was the case I'd never run a marathon.
7) Don't overtrain: This is a pretty simple one - of course it's sometimes hard to tell when you've crossed the line. Marathon training is so difficult that simply being tired might not be a sign to ease up your training. But, on the other hand, you can't ignore what you're body is telling you. If your pace is way off in workouts - or you're getting sick constantly you should probably back off.
8) Train the mind: People probably don't appreciate the importance of training your mind to overcome pain. Many runners who don't start until they are adults train at the same pace that they race. Of course, part of that is they are not necessarily competing - but, another part of it is that their minds are used to pushing their bodies as hard as someone who has been competing since they were a kid.
9) Rest before the race: As I said before, the taper is very important. Noakes argues that no other running writer seems to have said anything about tapering before Newton. In fact, many would run time trials just days before big competitions.