[FourthProtocol]

I'm somewhat surprised that strategy is only mentioned once (at time of writing). Strategy is vital for any leadership role. Sun Tsu is a classic, but can be difficult to assimilate. There are many resources on Wikipedia.

Often overlooked is dealing with power and politics (https://www.wittenburg.co.uk/Work/Politics.aspx)

Keeping up to date on tech also important, especially at the tech lead/architecture level (https://www.wittenburg.co.uk/Work/Mentoring.aspx).