Tough one... I don't think there's any one formula... because being successful as a Head Coach (anywhere) requires expertise in so many things:
Here's just a few things that I think need to be in place... but I'm sure there are more...
1] Have enough power to effect change... real change (even if you're a good HC... if you're a puppet, you can't do your job)
2] Hire an effective staff
3] Be able to manage downward and upward
4] Be able to effectively spot talented players
5] Be a good motivator to all in the organization
Like I said, you could be a great HC.. but, if one or two things are missing, then you are set up for failure.