I'll do my very best to give you a rough outline, but to the guys out there with first-hand information, please go easy on me. Most of what I've got comes from looking at the logs of the guys Squires coached and from hearing what my college coach, Bruce Lehane (who wrote a book with Squires and was one of his athletes back in the 70s) has to say on the subject.
Key points:
1) not killing yourself in training- very, very important
2) a good amount of volume
3) longer workouts with a decent amount of rest at aerobic type paces (short rest rarely utilized as far as I can tell)
4) for marathoners, a lot of "change of pace" type long runs. Look for Greg Meyer's logs before he won Boston in 1983. Lots of stuff like "3mi easy, 5mi fast, 1mi jog, 5x5xmin on, 1 min off, 1mi jog, couple miles steady, mile easy, mile on the track in 4:40, mile easy."
5) self-sufficient runners
A lot of his guys seemed to race fairly frequently; I'm not sure how much of that was by design, or his runners personal preference, or monetary reasons, or what. I'm guessing because it was fun to race and there are a lot of road races in New England! Also, I don't want to overstate how much emphasis Squires seemed to put on not over-exerting yourself in the workouts. I seem to recall Salazar saying that, as a high schooler, he would train with the Greater Boston guys and that you would never guess that Bill Rodgers was the stud of the group from the way Bill was content to run midpack in workouts and not kill the intervals.
Again, anyone with first hand information that contradicts me, please correct me. Also, the OP, you might want to check out the book Squires and Bruce Lehane wrote. You can find it at
www.speedwithendurance.com