Thousands of books have been written on leadership. In my limited experience, most of the books are redundant and a repackaging of the same fundamentals. This isn't bad - and sometimes the new angle is really helpful - but if you read one book by Jim Collins, Patrick Lencioni, and Ram Charan - you are pretty much there.
Recently I've discovered a simple skill that separates effective leaders from the rest of the pack; and ironically, it's written about very little. Effective leaders understand that every interaction is either building or eroding trust and they make intentional decisions to build it. This is especially true when meeting with senior leadership. The questions you ask - comments you make - body language - how you express yourself; it all contributes to]trust - which is everything.
Often very well-intentioned leaders erode trust. They are hard workers - invested - but make tragic mistakes in meetings that mitigate their colleagues and supervisors ability to trust them. When that goes unchanged for 12 months or more - it is time to make a change. Perhaps not a termination - but certainly a reality check about the future. Often this drives the employee out of the organization, which ultimately works to their benefit because they dive into a new tank and are forced to survive and grow; or be eaten. In that new environment they become more self aware and fix the fatal flaws.....and live happily ever after :)