I've read many startup/management books the last few years and I keep going back to High Output Management [1]. Andy Grove has really great insights about managerial leverage, influence, planning, the purpose of and how to hold meetings, and motivation vs. control. His perspective on one-on-ones has been especially useful as we scale.
[1] If you don't have time to read the whole book, I've taken some pretty detailed notes at http://charles.io/high-output-management/ :)