From personal experience working with a coach who got a lot of quality athletes, then ran them into the ground and blamed them when they didn't perform, here's things to look for:
1. Watch out for a coach who promises his that his school/program is the best_____(fill in the blank). This comes from a recruiting perspective. If a coach promises you that his school/program is the best whatever, he is over-selling it and you will most likely be disappointed. The next point goes along with this.
2. Look at the number of guys not in the top 7 or so. Are they improving? Are they even competing? There are a lot of "successful" coaches who are working with really talented, durable runners, but if look out of the top 7, the rest of the guys are injured, not progressing, have little motivation, and don't compete. The reason there are so many athletes on the team is the coach is a good salesman ("My school is the best...") and a lot of hs kids fall for that. Once they get to the school and are in the program, the fairy tale fades away quickly.
3. Talk to the other athletes on the team. Ask them DIRECTLY what they think about the school, coach, program. I believe the athletes on the team are the biggest indicator what a coach is like.