This recent memo from McDermott Will & Emery: "D&O Insurance—Issues to Consider Before a Claim Arises" does a really nice job of simplifying a complex topic without compromising the substance. The memo identifies the most common D&O coverage concerns and how they can be addressed at the policy initiation or renewal stages in a manner understandable to in-house and law firm counsel and corporate secretaries - regardless of prior insurance expertise.
Having learned from first-hand experience while serving in-house during particularly challenging times, this is one of those topics that can tend to be relegated to the "if/when I have time" pile due to your focus on a never-ending supply of real-time issues and fire drills - until something really significant and unexpected occurs, when D&O coverage immediately ripens into the most important item on your agenda and something that the board and management care passionately about (for good reason).
The memo is definitely worth a quick read and consideration.